I've been following this for a while now and have always felt that the MS suggestion that it is just a research project was a cover up for the fact that they're working on Windows successor. Well it appears to be taking shape.
Microsoft's plans for post-Windows OS revealed - Software Development Times On The Web
I'll drink to that ... well, I'll drink Midori for any reason.
... the real Midori ......
As a side note i didn't know about Codeplex, doesn't sound very MS.
CodePlex is Microsoft's open source project hosting web site
CodePlex - Open Source Project Hosting
Codeplex is very much what MS does!
If you take the view (and I couldn't possibly comment) that MS is just about taking control of the planet then having a site like this is perfect - it means that you get everyone else to do the work of showing why you should develop for Windows (rather than any of those other nasty OS)
You could also argue that it saves MS the hassle of trying to put together working code examples for any of their products (the stuff that used to be on MSDN) and just let other people do the work for you.
If you think of MS as being "embrace, extend, extinguish" then you might think that they're trying to do a sourceforge type thing but, basically, Windows only.
Well it's not just MS it's most large corps that's just how they operate, make it as hard for the competition as possible and maximise your shareholders return. It's the big failing with the stock market business model. I do know where you're coming from though but if people are willing to do this work for free why would MS pay for it? :)