Microsoft’s Jeff Toews (from the Microsoft.com Operations Engineering Team) talks about how Microsoft.com has been running on Windows Server 2008 since May of 2007.
They are running about 100 quad-processor, 32GB Web servers, that are geographically distributed in multiple data centers (Bay Area and Puget Sound). He discusses how they migrated from IIS 6.0, used WCAT to do performance testing, and some of the issues they ran into during the effort. He also talks about caching of dynamic content in IIS 7.0 Another great feature is Failure Request Event Buffering (FREB), which allows you to capture and debug failed requests without having to use WinDebug.
There is a lot of good information in this video podcast.