We use Windows Server 2008 on one of our test machines, and we have no problems so far with it. Once IIS7 is properly configured, everything is fine. As for security tweaks, we need ASP.NET worker process to have access to the Sitefinity's program files, and Forms Authentication enabled in IIS.
Let us know if you experience any problems, and we will give our best to help you right away.
All the best,
the Telerik team