I just noticed that vSphere has been added to the Windows Server Virtualization Validation Program:
Products that have passed the SVVP requirements for Windows Server 2008 R2 are considered supported on Windows Server 2008, Windows 2000 Server SP4 and Windows Server 2003 SP2 and later Service Packs, both x86 32-bit, and x64 64-bit.
Might come in handy when you need to get support from Microsoft….