Brad Garlinghouse’s appointment to a new job at AOL today as its new communications czar is yet another sign of an interesting trend for those keeping score of the comings and goings of top Internet execs.

Garlinghouse came to the Time Warner (TWX) online unit after a year-long break, preceded by six years at Yahoo (YHOO).

As anyone who watches the digital space knows by now, this kind of management musical chairs is common and never-ending.

In fact, borrowing a quote by IAC/InterActiveCorp (IACI) CEO and chairman Barry Diller from an onstage interview I did with him at the sixth D: All Things Digital conference and switching out Hollywood for Silicon Valley: “[It] is a community that’s so inbred, it’s a wonder the children have any teeth.”

But, given all the movement of late, this insider seat-switching seems more frantic than ever, as allegiances shift, competitors become friends and colleagues become rivals faster than you can tweet.

When he left Yahoo last summer, in fact, the digital chatter was that Garlinghouse would take a job either as a venture capitalist (he had been one once) or helming a start-up (that too, at Dialpad.com).

In fact, sources said, Garlinghouse had been considering two mobile gigs, but opted for helping to try to overhaul a troubled Web giant.

Fixing messes was the impetus of Owen Van Natta, who left a top job at social networking giant Facebook in early 2008 and by the end of the year, headed over to run Project Playlist, a controversial online music-sharing service.

But then he had hightailed it by spring to try his hand at reviving MySpace, as its CEO.

His boss, News Corp. (NWS) digital head Jon Miller, did the same, getting the hook (unfairly to my mind) at AOL several years ago and then creating an investment firm with former MySpace head Ross Levinsohn.

The pair considered being part of a bid to oust Yahoo management in 2008.

Miller’s freedom lasted only until he got an offer that he presumably could not refuse from News Corp. head Rupert Murdoch recently. (Full disclosure: News Corp. owns Dow Jones, which owns this site.)

The list goes on, chock full of ex-Yahoos, in fact.

Its one-time COO, Dan Rosensweig, left the company in 2006, for example, and joined the well-known private-equity firm, Quadrangle Group.

But, soon enough, he was scooped up by Activision Blizzard (ATVI) to run its Guitar Hero division.

Yahoo Network head Jeff Weiner also departed from the Internet giant, in mid-2008, for a stint at two VC firms.

He landed at LinkedIn, the business-networking service where he was named CEO in late June.

Greg Coleman ran Yahoo ad sales until mid-2007 before taking a job at AOL earlier this year, which he lost after it got new management soon after.

At Yahoo, Coleman sparked with former advertising sales head Wenda Harris Millard, whom he ousted. She went onto Martha Stewart Living Omnimedia (MSO) and left there this spring for the Media Link consultancy.

Presto! She is now helping MySpace’s Van Natta fix the social networking site’s ad business.

Current Yahoo U.S. advertising head Joanne Bradford actually came from Microsoft last summer, via her own short visit to the troubled ad start-up SpotRunner.

Former Yahoo search techie Qi Lu now runs digital for Microsoft (MSFT), along with a big gang of ex-Yahoo techies he has recruited.

And Scott Moore is even better at the switcheroo. He was at Microsoft running MSN U.S. content, switched to Yahoo as its media poobah, left last year to consider a start-up and then headed back to Microsoft as head of U.S. content this year.

But former Google (GOOG) execs have also been busy shuttling hither and yon, mostly to innovative start-ups.

Of course, many find refuge at Facebook (COO Sheryl Sandberg, PR major domo Elliot Schrage and many more) and Twitter (GC Alexander Macgillivray and COO Dick Costolo).

Recent departures–such as Sukhinder Singh Cassidy, who landed at Accel Partners for now–are also likely to find new homes soon enough.

And, of course, there’s always Garlinghouse’s new boss, former Google ad head Tim Armstrong, who took over at AOL earlier this year.

We’ll skip former Joost CEO and former Cisco (CSCO) exec Mike Volpi (who is now a VC); former Netscape Communications/short-term VC/ex-banker/current-for-now CBS (CBS) digital head Quincy Smith; and Joanna Shields, who has worked at Real Networks (RNWK), Google and Bebo (which was bought by AOL)–for now.

Because, around and around and around it always goes, as you can see in this funny video below, which I posted previously:

[Musical Chair designed by Jacob Mathew.]

[Updated with new details about deal, including who worked on it and info on a cash component.]

About three weeks ago, Facebook and Twitter ended several weeks of serious talks, in which Facebook was offering to acquire Twitter for $500 million of its stock, which also included a cash component.

While rumors of Facebook’s interest were brought up in an interview with Facebook CEO Mark Zuckerberg at the Web 2.0 Summit a few weeks ago, some shot down the idea as silly.

Quite incorrectly, as it turns out, since top execs at both Facebook and Twitter were right then at the tail end of discussions, which were initiated by the privately held Facebook in mid-October, about bringing the two together.

Those talks, sources on both sides said, are now over.

So why did the deal break down?

Well, as is usually the case, over price–was $500 million worth of Facebook stock actually worth $500 million?–and the typical concerns about integration and costs.

But, more important, it seems, was a feeling among Twitter investors and execs that the start-up should still take a shot at building its revenues–there are none right now–as well as it had done at building its growth.

“It’s more about timing,” said one person familiar with Twitter’s motivations. “There is a strong feeling that there is still an opportunity–even with the economic downturn–to blow this thing out.”

Still, combining the world’s fastest-growing social-networking site with what is quickly becoming the best-known microblogging service is actually a natural fit.

That’s especially true given that Facebook–for all its powerful online social connections–has seen Twitter race past it in innovating in the “status update” arena.

While some sources at Facebook said Zuckerberg was becoming frustrated by the buzz Twitter was getting–a market that should have been dominated by Facebook–others at the company said he was interested in buying Twitter because of his respect for its progress.

Indeed, at the Web 2.0 interview, Zuckerberg called Twitter an “elegant model” and said that he was “really impressed by what they’ve done.”

Indeed, with about six million registrations, as reported in October, up 600 percent over the last year, the San Francisco-based Twitter–launched in 2006–has had impressive growth.

(It has also been plagued by technical issues, which are–to be fair–decreasing.)

In any case, for those not familiar with it, the premise of Twitter is dead simple: A registered user logs in via the Internet or a mobile phone and answers the “What are you doing?” question the service asks in only 140 characters or fewer.

It’s quite a clever idea, although–so far–not a money-making one.

To try to goose that, Twitter’s board replaced the engineer who created Twitter, Jack Dorsey, with another founder, Evan Williams, who had served as its chairman and chief product officer.

The more experienced Williams (pictured here) had already built one company–Pyra Labs, which created the Blogger blogging service–that he sold to Google in 2003. He also started the audio and video search site Odeo, where Twitter was actually born.

Still, its investors have not come down on Twitter to hold back its growth efforts, and have handed over $20 million to the start-up so far. In its last round, Twitter was valued at $98 million.

Its funders include: Union Square Ventures, Charles River Ventures, Digital Garage, Spark Capital and Bezos Expeditions, backed by Amazon Founder and CEO Jeff Bezos.

In addition, well-known Silicon Valley figures, such as Marc Andreessen and Ron Conway, have also invested. Interestingly, Andreessen is also on Facebook’s board.

Other private investors include FeedBurner Co-Founder (and now Googler) Dick Costolo, former Epinions Co-Founder Naval Ravikant and former Googler Chris Sacca.

Twitter needs all the investors it can get, since it has no revenue, although it has been exploring things like charging business customers and adding advertising into the consumer service.

Lack of revenues was an issue for Facebook, said sources, especially related to fees Twitter pays for delivery of its messages to cellphones.

While the issue has been manageable in the U.S., Twitter cut off its SMS support in some international markets this summer because of too-high costs.

But, if Twitter was offered to Facebook’s 120 million users, Facebook execs estimated that it might have to deal with huge SMS fees–up to $75 million annually.

“Facebook has its own revenue-generating challenges,” said one person close to the company. “As much as Twitter would give them a lift in the status area, it was still a worry.”

Not enough, said several sources, to stop Facebook from making another approach at some point in the future. “We’d hate to see Twitter go to another company,” said one source.

Indeed, while all are even more price-conscious than Facebook, large companies that could also be interested include: Google (GOOG), Yahoo (YHOO), Microsoft (MSFT) or a large telecom company, such as Verizon (VZ).

If it had completed the deal to buy Twitter, it would have been Facebook’s most significant acquisition by far.

Zuckerberg and Williams did meet and get along well, but the deal was primarily negotiated by Spark Capital partner Bijan Sabet (Spark is a Twitter investor) and Facebook deal guy Dan Rose.

But in this time, at least, the Twitter side was still not interested in selling at the price Facebook had offered.

The $500 million offered was in an all-stock form, said sources on both sides, at the $15 billion valuation that came from the Microsoft’s investment in the company last October.

The Twitter side felt that figure was inflated and the shares should be valued at the lower figures that have also been reported for Facebook’s true valuation, more in the $5 billion range.

That would have given the deal a $150 million price tag, which was seen as too low, especially since it was in Facebook stock and not cash initially.

In fact, Twitter wanted cash, which some sources say was offered by Facebook in the $50 to $100 million range, in addition to stock, but taking too much stock was still a major issue.

There are other ways the pair could have approximated a safer choice for Twitter, via warrants, of course, or other methods.

But, said several sources close to Twitter, the primary reason for not selling was because its board simply did not want to yet or perhaps ever.

Said one source: “The question is, is it really a good idea to sell on the first chance you get?”

Well, for Twitter, we’ll just have to wait and see about that, of course.

[Photo of Evan Williams by Joi Ito. Licensed under Creative Commons 2.0 By-Attribution license.]