If you're still using the original Hyper-V that runs as part of Windows Server 2008, this is a big deal.

While Windows 7 is getting all the attention, the equivalent server version (Windows Server 2008 R2) is also available as a release candidate. This is how you'll get the latest and greatest Hyper-V.

As the dev lead for perf/scale development on the hypervisor, I can assue you that the improvements in Hyper-V in this version are substantial. Among the announced things are support for Intel and AMD's virtualization aware CPUs, which provide substantial performance improvements.

Plus, Hyper-V has a few more awesome capabilities up its sleeve. Stay tuned. :-)

Here's the official team blog link:

http://blogs.technet.com/virtualization/archive/2009/05/06/microsoft-hyper-v-server-2008-r2-release-candidate-free-live-migration-ha-anyone.aspx