Nick White from the Official Windows Vista Blog just posted some very interesting news. It appears that Microsoft actually has ears, and listens to the feedback it gets. While not budging on the fact that only Vista Business and Vista Ultimate are allowed to be used inside a Virtual Machine (it really does make sense, except for a few software testing-related edge cases), Microsoft has amended the terms of the Vista EULA to allow retail box copies of Vista to be transfered between machines an unlimited number of times.
It's important to note that the copy of Vista you buy on a new PC cannot ever be moved to another machine... just like in XP. That's not changing either.
Kudos to Microsoft for listening to the community. Now, about that Vista Family Pack...