Well, everyone else has been posting about the PDC - I thought that I would have written by now, but I haven't really seen anything that is really exciting. So far, most everything seems to be a refinement of things introduced in PDC 2003.
Oh, Office 12 was mentioned. Since use Office as a glorified Wordpad.exe, that's really not that exciting.
I am currently sitting in the session, "High Performance Computing with Windows Server Compute Cluster Solution." It's a slide-show fest, with very little demo or bits to see. This session is a basic review of of Clustering, and is mostly review if you are familiar with these concepts.
There's actually very little about what microsoft is doing in this space, and more about what high performance clustering actually is. I'm still not impressed. Show me, don't slide-show me.