[UPDATE: AOL confirmed our story below about Coleman's departure and Levick's appointment. See below.]

Platform-A President Greg Coleman–the former Yahoo advertising sales exec who came to AOL only three months ago–is leaving the company, sources said, as new CEO Tim Armstrong remakes his top staff in preparation to spin off the Time Warner (TWX) online unit.

Coleman was brought to AOL by former CEO Randy Falco in February, replacing Lynda Clarizio. But Falco was ousted two weeks after Coleman got there.

Armstrong, sources said, announced the moves to staff tonight, right after he told Coleman about his decision late today.

Coleman will be replaced by a Google ad exec, Jeff Levick, sources said, who had a close relationship with Armstrong when they were both working at Google (GOOG).

AOL said in a press release that Levick would become “President, Global Advertising and Strategy, a new and expanded role, in which he would be “responsible for Platform-A, AOL’s advertising business, as well as developing global revenue strategies.”

Levick will be the third major Google advertising exec to leave the company recently, after Armstrong himself and today’s departure of former DoubleClick boss David Rosenblatt.

Levick (pictured here) was a VP of industry development & marketing, the Americas. He has been at Google since 2001.

Also out: CFO Nisha Kumar, who came to AOL in early 2007 from Time Warner. She was told of the decision earlier, and there has been a search on for her replacement.

It is a time of much change at AOL. Yesterday, Time Warner reiterated its intent to spin off AOL in a regulatory filing, and to buy back the five percent stake Google owns.

Time Warner also had to deliver bad news about AOL’s disappearing ad revenue today in its quarterly earnings report. It was down 20 percent.

Its ad business has not been helped by the fact that AOL has seen a number of Platform-A heads roll over the last two years.

Coleman is an experienced online ad exec, who was at Yahoo (YHOO) for seven years, responsible for all advertising revenue worldwide. He came to Yahoo from Reader’s Digest.

But Coleman ran into Yahoo’s management buzzsaw after trouble hit the company in 2007. He was one of the first in a long line of execs to leave the troubled company, departing in one of its many controversial reorganizations.

But Yahoo’s ad business did grow strongly under him and former Yahoo ad exec Wenda Millard. She was also pushed out of Yahoo and just left her job as co-CEO of Martha Stewart Living Omnimedia.

Before AOL, Coleman had been running a Los Angeles-based start-up called NetSeer, which focuses on ad targeting.

While at AOL a short time, Coleman had busied himself reshuffling the staff there in several moves.

He has a three-year contract, sources said, which AOL will presumably have to pay out on.

Here is the official AOL press release:

JEFF LEVICK NAMED HEAD OF AOL GLOBAL ADVERTISING AND STRATEGY

New York, NY–April 30, 2009–AOL announced that Jeff Levick will join the company as President, Global Advertising and Strategy. In this new and expanded role, Levick will be responsible for Platform-A, AOL’s advertising business, as well as developing global revenue strategies. Levick comes to AOL from Google, where he was most recently VP of Industry Development and Marketing, The Americas. He will report directly to AOL Chairman and CEO Tim Armstrong.

“Our goal at AOL is to create great content and products, as well as make our advertising offerings the best in the industry for marketers and we are putting together the strategy to achieve that. I’m delighted that Jeff will be coming on board to lead this effort,” Armstrong said. “I’ve worked with Jeff for more than seven years at Google, and he is absolutely the right person to drive growth in our premium ad sales, dramatically scale our Advertising.com business, and further develop AOL’s research initiatives and consumer insights.”

“This is a perfect time to join AOL and I firmly believe that AOL’s best days are ahead of it,” said Levick. “The company has one of the largest and most engaged audiences on the Web, some of the best advertising technology in the business, and a powerful third-party network. There is great opportunity here for us to capture.”

As a result of this change, Greg Coleman will be leaving Platform-A, where he has served as President since early February 2009.

“In only a short time, Greg made a strong imprint on Platform-A’s sales organization–reorganizing and refocusing the team,” said Armstrong. “I appreciate his efforts and know that they will contribute to the work that lies ahead with Platform-A.”

Levick will officially join AOL in the coming weeks. At Google, Levick was responsible for business marketing activities for the Americas as well as sales development and strategy for all of the vertical industries covered by Google’s Americas sales organization. Levick joined Google in 2001 and has held various executive management positions in the company’s advertising sales organization in both North America and Europe.

Prior to joining Google, Levick served as a corporate attorney with a specialty in mergers and acquisitions at the international law firm of Katten Muchin Rosenman, and held roles at various online ventures in Chicago. He currently serves on the board of directors of Helium.com, the advisory board of the College of Communications at DePaul University and as an advisory board member of the global trade organization Search Engine Strategies (SES). Levick holds a J.D. from DePaul University and a bachelor’s degree from New York University, where he graduated cum laude.

The game of executive musical chairs among Web companies keeps on going, with sources telling BoomTown that AOL ad head Lynda Clarizio will be departing the online service and replaced by former high-ranking Yahoo ad exec Greg Coleman (pictured here).

Last week, this column first reported on former Yahoo media head Scott Moore taking a similar content job at Microsoft (MSFT), which had been vacated by Jeff Dossett, who took Moore’s job at Yahoo.

The less confusing move at AOL, with Coleman taking over for Clarizio and which has been in the works for only a week, could be announced as early as today, although I have been hearing rumors of such a development since late last week.

Clarizio has been head of Platform-A, the overall name for AOL’s advertising business, which includes a lot of various online ad companies AOL has bought in recent years.

She had been running AOL’s Advertising.com in Baltimore before being tapped to integrate them better over the last year, after a series of ad execs shuffled in and out of AOL.

But, said several sources, as a former AOL lawyer and dealmaker, Clarizio (pictured here) is not regarded by top execs the kind of nitty-gritty sales exec that AOL needs now, as it seeks to revive its fortunes.

AOL’s ad business has lagged badly of late, with owner Time Warner (TWX) pre-announcing that the online service’s results would be particularly weak this quarter. Time Warner reports quarterly earnings tomorrow.

Since a much-chewed-over possible merger with Yahoo (YHOO) has been put on ice, with the recent arrival of new CEO Carol Bartz, Time Warner and AOL execs have decided to focus on strengthening the online service and making much needed changes.

AOL recently announced a 10 percent layoff of its staff of 7,000, part of the rightsizing that has been going on.

And its valuation was also recently written down by Google (GOOG), to $5.5 billion from $20 billion several years ago.

AOL had already been in the midst of renovating its communications and social-networking assets under a new division called People Networks, which is run by former Bebo head Joanna Shields.

Its content arm has also gotten a different blog-centered direction and name–MediaGlow–under Bill Wilson.

Now, it’s apparently time for the ad leg of AOL’s three-pronged new strategy its future business is resting on to be fixed.

The hiring of Coleman came suddenly, said several sources. He had been considering a top job at another well-known online company and also was planning to move to a start-up he has been running to the Silicon Valley area.

He was hired by AOL CEO Randy Falco, whom Coleman has known for a long time, only last week, after Falco heard that Coleman was considering other positions.

Sources at Yahoo said the hiring had to be cleared by the company and Bartz, at Time Warner CEO Jeff Bewkes’s request, due to competitive issues.

Coleman is indeed an experienced online ad exec, who was at Yahoo for seven years, responsible for all advertising revenues worldwide. He came to Yahoo from Reader’s Digest.

But Coleman ran into Yahoo’s management buzzsaw after trouble hit the company in 2007. He was one of the first in a long line of execs to leave the troubled company, departing in one of its many controversial reorganizations.

But Yahoo’s ad business did grow strongly under him and former Yahoo ad exec Wenda Millard. She was also pushed out of Yahoo and now is Co-CEO of Martha Stewart Living Omnimedia.

Since then, Coleman has been running a Los Angeles-based start-up called NetSeer, which focuses on ad targeting.

Given his media background, Coleman is likely to be key to expanding premium branded advertising display sales across AOL’s advertising and programming networks.

He will move to New York and report to AOL President and COO Ron Grant, said sources, although Platform-A has key offices in Baltimore and San Francisco too.

It is not so apt, if you think about it, that Yahoo has finally put up the details of its new system to let customers buy and sell display advertising–now called APT–right smack in the middle of the most serious financial meltdown of the modern era.

That’s because the economic crisis is likely to become a whirlpool that will be hard for any ad business to avoid, even the often recession-proof digital sector.

But it is Advertising Week in New York and, BoomTown supposes, the show must go on (it’s not as if they could suspend it, like a critically important Presidential debate or anything).

Actually, “ironic,” I suppose, is a better word than “apt,” because the existence of such a system–as a kind of Google-like way to deliver graphical advertising–is extremely vital to the next phase of the online ad game.

In Yahoo’s case, APT would service its sites, as well as big sites like eBay (EBAY) and several hundred newspaper sites, in what one can only hope is a cohesive manner rather than the patchwork way it is done now.

In order to reach many places across the country, for example, a national advertiser now has to potentially make hundreds of buys, which can be highly inefficient.

The other option is to use one of the too-many ad networks. But they often don’t let an advertiser know exactly where an ad is being placed, and it can sometimes create something called “channel conflict” between a publisher and an ad network.

This chaos has long been a problem in the online display business, which has been growing, although not with the same force or overall impact as the search ad business dominated by Google (GOOG).

Thus, the situation begs for clarity and for getting scale built into the system, which can only be imposed by big players like Yahoo (YHOO)–or Google or Microsoft (MSFT), both of which are working on their own systems.

Unfortunately, while the search ad market has a better chance to weather the current economic crisis, the online display market is a horse of a different color.

Many speakers at Ad Week underscored the obvious.

Former Yahoo ad head Wenda Millard, now co-CEO of Martha Stewart Living Omnimedia, said in a panel that the Wall Street crisis will have “pretty severe implications for medium-sized and smaller businesses and consumers.”

It was an opinion expressed by many others in the online space who attended the event, most of whom also tried to note in some fashion that the digital sector has a better chance to weather the expected slowdown than other media like magazines.

That might be so. But as one top digital exec correctly noted to me after the events of this week, which have deeply impacted banks and Wall Street firms, it will be hard to escape the suction-like pull of sinking ships:

“Like it or not, we’re all financial stocks now.”

Millard (pictured here) went to MSLO after many years of building and running Yahoo’s (YHOO) ad business (previous to that stint, she worked at DoubleClick in its earliest days).

She was also recently made chairman of the Interactive Advertising Bureau, the prominent interactive ad trade group.

Nonetheless, Millard left Yahoo under a cloud, as she and the company parted on the way online ads should be sold going forward and then got into a bit of a tussle of just who left whom, especially with Yahoo President Sue Decker.

Without going into the complicated and conflicting details, some of which became personal and became very public, it was definitely not the way Yahoo should have rewarded Millard–who is well-liked and well-known in the ad industry–after years of loyal service.

As I wrote in a post on her Yahoo departure a year ago:

But I did have an idea about how cloddishly that Yahoo could handle Millard’s departure, in a vain attempt to make it look like they are on the ball in a time of management turmoil that seems only to roil and boil more as time goes on. The decimation of executive ranks there is like watching an online version of “Ten Little Indians,” or for you kids, “Hostel.”

And when you badly treat an employee who has worked pretty hard over the years for you as Yahoo did Millard, you have to wonder how in the world the company is going to attract top talent from the outside–let alone keep those valuable employees on the inside from bolting.

But Millard’s departure–which seems to be a case of her looking for and getting another job, all while Yahoo was also rejiggering its approach to ad sales–was handled with no grace and much confusion.”

Sounds like a bit of a broken record for Yahoo by now; as it turned out, Millard became one of the first in a long line of Yahoo execs to head for the exits.

Millard first went to MSLO as its president of media and got the top job (jointly with Merchandising President Robin Marino) after former President and CEO Susan Lyne stepped down.

There she will have to focus a lot on MSLO’s online business, which is probably its best bet for future growth.

The company needs it, as it has been clawing its way back to better results of late. MSLO stock has been dropping since 2007, all the way to close to $5 a share, although it seems to have stabliized more recently in the mid-$7 range.

It is a good thing–oh, I had to–that online advertising is a topic Millard knows well.

In fact, she actually likes talking about the block and tackle of figuring out how to properly use commercial messages within the online space.

At Yahoo and today, she was well known as a backer of brands over the holy algorithm and has often railed against treating online ads as if they were pork bellies–that is, commoditizing the business.

Here’s the video of her talking about it and more:

While Stewart is known for her focus on home-making skills, some might not know that she is also a bit of a geek, who has been a fixture at many tech events over the years.

For example, she has been an active audience member at our D: All Things Digital conference over the last two years (here she is at D4, grilling Sony CEO Howard Stringer about why there had to be so many wires with her devices).

In this interview with WSJ Online, she talks about her company, Martha Stewart Living Omnimedia, including its many forays into the Internet area.

That will soon mean a new site she has dubbed “Marthapedia,” or–as BoomTown likes to call it–”All Things Martha.”

She has apparently grabbed Vice President of Sales Strategy Jacki Kelley (pictured here), who one Yahoo wrote me “was one of the good ones.” It’s unclear what role Kelley will have at Martha Stewart Living Omnimedia, where Millard landed this summer as its president of media.

[UPDATE: Kelley will be EVP of media sales for MSLO, running all sales for digital, magazines and broadcasting, a move that keeps her full-time in NYC. One reason she left: sources say Kelley was tiring of all the travel back and forth to Sunnyvale with all the Yahoo reorgs.]

Sources at the company said Kelley is not the only one taking off in the upcoming few weeks (and last week brought the departure of marketing head Cammie Dunaway to Nintendo and also longtime PR exec Joanna Stevens).

Here’s the late Friday memo from Yahoo Executive Vice President Hilary Schneider on the Kelley departure:

From: Hilary Schneider
Sent: Friday, October 26, 2007 8:33 PM
To: [XXX]
Subject: Sales Announcement

It is with mixed emotions that I am announcing that today is Jacki Kelley’s last day at Yahoo!. Since joining Yahoo! in May 2006, Jacki has led our advertising efforts for the travel category and has recently played an integral role helping to facilitate the integration of Yahoo!’s search and display sales teams. Please join me in thanking Jacki for her contributions to Yahoo!, and in wishing her the best of luck in the next chapter of her career.

To ensure a smooth transition, Jacki’s directs will report to [Dave Karnstedt] on an interim basis. The Advertising Strategy teams have done some great work, and our commitment to their efforts will continue unabated.

We’re making great progress on integrating the Sales Team, as well as with work we’re doing to ensure greater focus across the entire Global Partner Solutions division. The work we are doing now to align around customer needs will accelerate our ability to deliver the most value for our advertiser and publisher partners.

Thanks in advance for your continued focus.

Hilary