Microsoft's virtualization-friendly Vista Enterprise license
"The main feature of the VECD license is that it is instance-based, not installation-based. What that means is that with VECD, Vista is licensed per user or use, rather than per installed copy. A Vista VM, therefore, can be dynamically moved between virtualization hosts, and organizations can store VMs offline without requiring that they be fully licensed."
Read the entire article here.
Update: Read Brian Madden's comments on this here.
Update: Microsoft Enables New Ways to Deploy Windows Vista
"New options to license desktop virtualization and diskless PCs give Windows Vista Enterprise customers more choices, says the director of Microsoft's Windows Business Group."
Read all about it here.