This week, Microsoft released beta 2 of its Service Pack 2 for Windows Server 2008 and Vista operating systems. If you're so inclined, you can download the 32-bit version or the 64-bit version to test on your systems. YMMV, of course, as these are intended for testing only and not for production systems. So go ahead and check 'em out in your sandbox.
According to Microsoft, the Service Pack is intended to improve performance and stability, increase hardware support and make it easier to manage both products in large deployments.
It's interesting to note that both Windows Server 2008 and Vista are now based on the same code, so they get the same service packs.