Interesting article on virtualization.info regarding MSDN and Technet being hosted on Hyper-V virtual servers. The SQL backend however is still being hosted on physical servers.
Technet received about 1 million hits per day, and MSDN about 3 million so obviously MS think that Hyper-V can handle the load 🙂
More info can be found here:
http://www.virtualization.info/2008/05/microsoft-migrates-msdn-and-technet-on.html