Not working yet that I know of....
Unless you include running Windows Server 2008 inside bootcamp. According to Adam Shepherd, it works fine there as you would expect. What I was hoping for was to have Hyper-V be the supervising OS, like some of the VM-Ware demos I've seen seem to, that can virtualize any OS that will run on the Intel Mac hardware (Server 2008, Vista, Mac OSX, whatever). So what Adam got to work is: Boot camp prompts for Mac or Windows and toot time. If you choose Windows, it boots to Windows Server 2008 with Hyper V funtioning as fully as on any hardware. So it may be what some of you are looking for.
Hope that helps and I'll let you know if we get more to work.
All the best,
Kevin Q.