BTW, RC1 of Windows Server 2008 is released. AFAIK, this is the last release before RTM.  Expect to see the official launch Feb 28th.

You can upgrade from RC1 to RTM! So if you've been avoiding Beta releases out of concern for stability, RC1 is is solid. (Actually, the server was really solid around beta 3).

Lots of new things to be excited about including an improved TCP/IP stack that should dramatically increase file transfers between Vista/Server and Server/Server. 

http://www.microsoft.com/windowsserver2008/audsel.mspx

BTW, the bits for SP1 of Vista share a lot in common with server as they are same the code base. As a result, Vista benefits from a lot of work done on Server and visa vera.  In the case of IIS 7, you will also get some new features.

=brett