I had a question today at a Virtualisation event about a feature by feature comparison of Hyper-V and other virtualisation offerings.  I had a quick search around and came across this 3rd party appraisal of all the different products out there on the market.  Now although this may or may not be completely accurate it gives a pretty comprehensive line up from all the main vendors - just to clarify it's not an official Microsoft statement.

Check it out here: http://www.it20.info/misc/virtualizationscomparison.htm