Out of curiosity, why was Vista such a big disappointment?
It was years after schedule, there were broken promises (which end users weren't aware of) and ugly is subjective, but I never found it to be slow.
Windows 7 only seems slightly faster than Vista, but is much, much faster (both in GUI responsiveness and disk/network IO) than Snow Leopard and Lion on the same hardware.
It seems like more than actual disappointment in Vista, people didn't really see a pressing need to upgrade to Vista, as XP, with all its warts, worked fine for their purposes.
It was disappointing for me because of the broken promises - the PDC 2003 video shows a very impressive GUI with skillful use of animation. WinFS would also offer vastly improved file management. Finally, being heavily based on managed code would make it both more secure and easier to develop for. But I agree most prospective Vista users were not aware of any of this. I, however, was.
FOr most users, the disappointment came from the "Vista Ready" sticker on computers that could run XP very well, but were barely capable of running Vista at acceptable speed and the Aero look.
BTW, his crashes may be hardware (memory) related. I'd advise him to run memtest or to take his Mac to the nearest Apple store to have it checked.