More musical chairs at Yahoo, which BoomTown predicted recently, as top execs at the company move in and out of jobs, and new ones from the outside move in.

Perhaps the most important change to occur is the replacement this week of SVP Scott Dietzen–who has been in charge of all communications and communities products at Yahoo (YHOO)–by former Adobe Systems (ADBE) exec Bryan Lamkin, several sources said.

Lamkin will become SVP of Applications Products.

According to his profile on LinkedIn, Lamkin (pictured here) was most recently SVP of Creative Solutions, Adobe’s largest business unit, where the software exec “led product strategy, marketing and product development for Adobe’s flagship software applications, including Photoshop, the Creative Suite, Dreamweaver, Flash and Illustrator.”

Lamkin, who was at Adobe for 14 years, has more recently been an executive-in-residence at two venture firms, New Enterprise Associates and Sutter Hill Ventures.

He will take over for Dietzen, who came to Yahoo in 2007 after its $350 million Zimbra open-source email acquisition

Dietzen–whom sources said is more entrepreneurial than managerial and did not want to lead such a big organization at the Internet giant–will become VP of strategy in the move. Many said they expect he will eventually leave Yahoo to try his hand at another start-up.

His colleague, Zimbra founder and CEO Satish Dharmaraj, left Yahoo earlier this year to join Redpoint Ventures as a VC.

In his job since, Dietzen has been busy fixing Yahoo’s mail and calendar offerings. (See my video interview with him below from last fall.)

But that’s not all.

Also afoot is a restructuring of Yahoo’s North American sales unit, with the unexpected promotion of Mitch Spolan, who was a regional sales exec and will now be in charge of all North American field sales.

The paidContent Web site reported the sales changes first, which have been rumored around Yahoo recently.

Spolan jumped over two more senior execs, sources said, who run sales operations for the East and West coasts. One of those execs, Beth Lawrence, will now run Yahoo’s relations with agencies. Both report to U.S. sales SVP Joanne Bradford.

Over the last 18 months, Yahoo has seen a bleeding of its advertising staff to a wide range of Silicon Valley Web companies, including, most recently, Yahoo’s VP of Sales Operations Dan Foehner to social-networking site Facebook.

Lastly, one of Yahoo’s most senior communications execs, Brad Williams, was let go as part of its recent round of layoffs. He had been running PR–admirably and with good cheer, I might add, despite all the bad news–since its head, Jill Nash, departed earlier this year.

Williams’s departure was first reported by The Wall Street Journal tonight. He came to Yahoo in early 2008 from eBay (EBAY).

New marketing head Elisa Steele, who was hired by CEO Carol Bartz, had recently hired a headhunting firm to find a new PR chief, sources said, and Williams was not considered as a candidate for the job.

UPDATE: Yahoo confirmed my report above.

A spokesman sent me the following info about Lamkin’s appointment:

Bryan Lamkin, formerly of Adobe, is joining Yahoo! as senior vice president of Applications Products, reporting directly to Ari Balogh. As a reminder, the Applications Products group consists of several key global products for Yahoo!, including Yahoo! Mail, Yahoo! Messenger, Flickr, Yahoo! Answers, Yahoo! Groups and Zimbra.

Bryan brings a wealth of experience on the consumer technology front and his background ties in nicely with Yahoo!’s ongoing focus to deliver great consumer experiences across the globe.

Bryan takes over for Scott Dietzen, who was named the interim head of Application Products following the reorg back in February. Scott will continue on at Yahoo!, and will work across Yahoo!’s Applications Products in a new product strategy role.

Bio

Bryan Lamkin

Senior Vice President, Applications Product, Yahoo!

Bryan Lamkin joins Yahoo! as the senior vice president of Applications Products. In this role, he will oversee the global strategy, development and performance for key products within the Yahoo! portfolio, including Yahoo! Mail, Yahoo! Messenger, Flickr, Yahoo! Answers, Yahoo! Groups and Zimbra.

Lamkin most recently served as senior vice president and general manager of Creative Solutions, Adobe’s largest business unit. Lamkin led product strategy, marketing and research and development for Adobe’s flagship software applications, including the Photoshop, Photoshop Elements, the Creative Suite, Dreamweaver, Flash and Illustrator.

In his 14 years at Adobe Systems, Lamkin held key management positions including Senior Vice President and General Manager, Digital Imaging and Video and Vice President of Marketing, Professional Publishing Solutions. Lamkin was responsible for product development and marketing as well as the acquisition and product integration strategies that established Adobe’s overwhelming leadership in digital imaging and video and web publishing. Before joining Adobe Systems, Lamkin served in key product marketing and international product development roles at Software Publishing Corporation and holds both a BA and MBA from the University of California at Berkeley.

And here is Dietzen in my video interview:

Well, here’s a good reason not to write off Joost quite yet: When the London-based company officially debuts its new Web-based service in mid-October, it will have some pretty hot content with its half-dozen seasons of the former NBC hit, “Friends.”

Also, there will finally be no more irksome plug-ins.

In other words, anyone with an Internet connection can watch streaming television shows and movies on Joost, with advertising embedded in various forms.

There will also be social-networking elements–you can see what your friends watch and form groups, make comments with cool tools and the rest of that sort of thing.

While all this is not going to make up for the lost time the online video service has wasted with its annoying P2P-based desktop client download, going to a Web-based, all-Flash service with more robust content is certainly the right way to stop rival service Hulu from continuing to clean Joost’s clock.

Joost was first out of the gate last year with a giant slug of funding, fancy founders (Janus Friis and Niklas Zennström, who were also founders of Web phenoms Skype and Kazaa) and blue-chip investors (Sequoia Capital, Index Ventures, as well as CBS, Viacom and wealthy Hong Kong investor Li Ka-shing).

In any case, Hulu quickly grabbed the lead in terms of press praise (I ate my words even!), ease-of-use and, most importantly, user numbers.

In the most recent stats, for example, Hulu had more than 100 million monthly video streams and 3.3 million unique monthly visitors. (But since Joost has just soft-launched its new Web-only service, it’s hard to make comparisons just yet, although the competition is now clearly afoot!)

And, although it has been written off by some, I do not think it is too late for Joost.

First, it is still early in the premium online video game.

Second, success will depend on having increasing amounts of quality content. And Joost–with CBS, Warner Bros., Sony and other unusual content like anime–certainly can keep up with Hulu’s programs from its partner parents, News Corp. (News Corp. is the owner of Dow Jones and this Web site) and NBC Universal.

Lastly, despite decent consumer uptake, the business is still in its nascent popcorn-stand stage of revenue and profit generation.

And while spending too much money and having too many employees did not help Joost, it seems as though CEO Mike Volpi has finally gotten control of the start-up beast.

Thus, while in London this week, I stopped in at the offices of Joost (near the famed King’s Cross train station, where, of course–to no avail–I tried to make it through the wall at Platform 9 3/4!) to chat with Volpi about all the changes at the much-hyped company.

Here’s a longish video, in which the always-well-turned-out former Cisco exec talks about all that and more: