With the virtualization wars getting hot, MS couldn't wait to release this I have no doubt.  You can download the server core and hyper-v for free just like VMWare's Esxi.  We don't espouse a Windows-only philosophy, but for a Windows-only shop, this is the key everyone's been waiting for.  However, unlike Esxi (which is also free), there are some "gotchas" - the most important of which is the processor.  It MUST be 64-bit and ALSO must have the hardware-baked-virtualization enabled Intel VT or AMD-V (for example, see http://www.intel.com/products/processor_number/chart/core2duo.htm to see if your processor measures up).   This puts old hardware out of the picture for this, so VMWare wins if you're consolidating old hardware.  We'll be playing with this over the coming months to see what else is there and give you our findings here!

Here's the info if you want to play:
http://technet.microsoft.com/en-us/library/cc732470.aspx
http://www.microsoft.com/downloadS/details.aspx?FamilyID=5da4058e-72cc-4b8d-bbb1-5e16a136ef42&displaylang=en

http://www.microsoft.com/servers/hyper-v-server/how-to-get.mspx