You may already know that you get some real benefits by pairing up SQL Server 2005 on Windows server 2003. You get to tie out SQL Server accounts to some of the Windows Security Policies, for instance. This trend continues with SQL Server 2008 on Windows Server 2008.
It's hard enough keeping up with all of the changes in SQL Server, so learning about all the new features in a new OS is something most of us don't have time for. But you should read a few of the highlights, or attend presentations at TechEd to pick up what you can. There are some really cool changes I'm seeing in Win2K8 that I think will help speed up SQL2K8. I'll mention some of those in future blogs as I run across them.