Microsoft has announced supportability status of Microsoft applications running in virtualized environments.

You can find the official statement here :

KB957006 - Microsoft server software and supported virtualization environments

You can find additional information on the Server Virtualization Validation Program (SVVP) page to find participant vendors.

KB944987 - Support partners for non-Microsoft hardware virtualization software 

And last, an updated version of the next KB article :

KB897615 - Support policy for Microsoft software running in non-Microsoft hardware virtualization software

~ Guillaume