Vista was not a very well-received release, but I remember using 64-bit Vista way back when. Maybe my memory is failing me a little, but I don't really recall Vista being that bad or unstable. UAC, of course, was a little annoying then, but 7 felt a little more unstable and crash-prone than Vista. My dad still uses a Vista desktop regularly (a 2007 install) and as far as I can tell it still works perfectly fine for h…
UAC issues cleared up once all of the software developers got around to releasing the next versions of their applications, but MS took most of the blame. I can't really blame the developers for not wanting to make significant changes to their software before the final release of Vista, given the chain of events leading from XP to Vista. Many are already hard pressed to remember how rocky the XP release was, and that MS did much more in XP to make 3rd party applications work with the system. In Vista they essentially took the extra step to warn the user that the application was misbehaving, rather than silently letting it happen. Some people got into the habit of disabling UAC by default and I had to convince one person who should have known better that he wasn't going to suffer from a deluge of support calls if he stopped disabling it in Windows 7 (and the handful of Vista systems still around).
In the end, 7 put very little in terms of functionality or stability on top of Vista SP1, though Microsoft did put significant work into making it possible to run 7 on systems that didn't have the horsepower for Vista. The marketing push brought a lot of people around. I look at it as an essential part of the strategy they're currently using with Windows 10 (vs. 8), though they took the extra step of changing the underlying version number this time around (something they didn't do when going from Vista to 7).
The biggest problems with continuing to run Vista are that the support window is rapidly closing and 7 will usually perform better on the same hardware (because they toned down the UI and put real effort into getting 7 to work on hardware that was previously running XP).