Microsoft has released the Hyper-V integration Linux drivers as GPL v2.

http://news.cnet.com/8301-13505_3-10290686-16.html

This is pretty cool news. I've been using Hyper-V, and for the most part, I like it. It isn't as full-featured as VMWare, but it is cheap, and nicer than any of the Linux solutions.

The biggest drawback has been guest OS. Suse included the driver, but any other Linux distro runs a bit slowly (and Fedora requires a hack).

Hyper-V isn't suitable for all situations, but this helps expand it.