Microsoft's Vista licensing will make use of Parallels (OS X) and other non-Microsoft virtualization solutions prohibitively expensive.
Other than enriching Microsoft's virtualization solutions and breaking all the competition, why would a convicted monpolist do this? Isn't Microsoft risking a return trip to the courts? (True, they found a way around those pesky American courts, but there's still Europe.)
Virtualization breaks Microsoft's Digital-rights-management and licensing models. If you authenticate your XP license in a virtual enviroment, then it will be authenticated in that virtual environment no matter the underlying hardware. So, one license, many machines. It's the same problem with their software license, their DRM copy protection etc. You can have one machine run a dozen instances of Word, and as far as each instance knows it's the only copy running.
Virtualization is a terrible threat to Microsoft's basic business. This will be war.