That's an SEO and usability suicide. Heck, Adobe owns Flash and yet pretty much all of their pages are in (X)HTML/CSS. They're smart enough to understand what the place for these in-browser technologies is.
My guess is that they'll use it at first for sound / video content. I would venture to guess that they'll bundle it as part of MSN Messenger at some point in the future as well, since it's a small addon to the .net runtime.
They use it at http://channel9.msdn.com/ which has prevented me from viewing a podcast or two, which I otherwise would.
MS used flash in their home page in the past, if I'm not wrong..
They've used Flash all over the place for product presentations and adds.