The Remote Desktop team just did an interesting post here:
About the RemoteApp for Hyper-V functionality that is available with Windows Server 2008 R2.
The concept here is that you would have a setup similar to Windows Virtual PC, where you run a legacy application in a Windows XP / Vista virtual machine, and access it seamlessly from your desktop. Only in this case the virtual machine is not running on your desktop – but on a Hyper-V server.
This looks really neat – and I am hoping to get the time to try it out in the next week or two.