This seems like a basically nice idea to me, although I do rather suspect that this means the discs sent by OEMs will get even more useless than they are now (already, a lot of them don't really let you do clean installs). I personally am not a big fan of doing the analogues to delocalizing on OS X and so on. I've used too many Windows machines where the discs are god-knows-where and OS pieces are missing. I'd rather MS just install the whole OS....
Did I understand correctly, though, that a home user could use the WIM architecture with their home copy of Vista to set their computer up just the way they want it, and then make a WIM image of the drive as installed? That would be sweet. It would sort of integrate the features of CCC or SuperDuper into the OS.
The only thing I would like to see (sorry, it sounds fanboyish, but it was something I really appreciated the first time I did an OS X install) is an analogue to archive and install. I think that feature is a gem.