Microsoft has released a 26 minute webcast about its virtualization licensing.  Thanks to Alessandro Perilli over at virtualization.info for the heads up.

The video is presented by Eric Jewett Lead Product Manager for Windows Server Marketing.  Jump to 18:24 to see an interesting analogy using coffee cups and moving VM instances between hosts, aka VMware VMotion or Microsoft Quick Migration:

Obviously, Data Centre is encouraged as the best licensing option.