I am a huge fan of Windows Server 2008. I am lucky enough to have a laptop that supports Hyper-V and has 4Gb of RAM so I have a dual boot setup for Vista and Windows Server 2008. I could just have Windows Server 2008 installed and then virtualise Vista on top, but there there aren't the integration components (like virtual machines additions for virtual PC, but for Hyper-V) for Vista yet so although it would run it wouldn't be that fast. Also James tells me that their will be some upgrade issues moving a hyper-V virtual machine created in the beta version included in the Windows server 2008 rtm to the Hyper-V rtm again around these integration components.
Anyway back to SQL Server. SQL Server 2008 ctp4 wouldn't work properly on the Windows Server 2008 beta around at the time; you had to remotely manage it if you wanted to use it. That was fixed in CTP5 and with the release of Windows Server 2008 I now run my demo's and tests on that.
Of course it's easy to setup a demo environment, you run everything as administrator and everything just works. In the real world you are going to need to secure and manage your data, and with many IT Pro's doing more than one job (part time dba, exchange and network managers to name a few) I thought it be worth having a look at this white paper on running SQL Server 2008 over Windows Server 2008. It's a high level document showing you what to use in each server to make your lives easier, if you are not an expert in the other server (like me!).
In a bizarre postscript I have a just built a virtual machine with 3 instances of SQL Server running on 32 bit windows server 2008, not that amazing except that the instances are called shiloh, yukon and katmai in honour of the version of SQL Server they relate to; so I have SQL Server 2000 sp4 running over Windows Server 2008. It gives me one place to show all the upgrade tools you can use to move from SQL Server 2000 to 2005 and or 2008 at next week's big launch event at the Birmingham ICC.