When I'm not messing with WPF and SL, I write software that needs to run on servers (behing WCF endpoints, usually.) I started experimenting with using Windows Server 2008 directly for this purpose, and I'm pleased to report that this experiment was quite succesful. What many folks don't know is that you can get the full desktop UI experience working on Windows Server 2008 (complete with Aero Glass if you like.)
There are detailed postings out there that tell you everything you'll need to do for this (such as http://blogs.msdn.com/vijaysk/archive/2008/02/11/using-windows-server-2008-as-a-super-desktop-os.aspx ), but the twist I'd like to mention here is that this even works on my vintage 2006 iMac (I keep an OSX machine around mostly to test for cross-platform compatibility in web sites, plug-ins, and document rendering.) I had been hesitant to dual boot a server OS there, but I need not have feared - the install went seamlessly. No troubles with VS 2008, SQL 2008 Feb CTP, or the Silverlight 2 Beta there either.
The only compatibility issue I ran into was with the Windows Live Messenger - the installer didn't like the OS version (and I haven't found a workaround yet.)
If you're developing for the server OS, you can expect a friendly environment there waiting for you.