Most competitive shooters don't suffer from screen tearing that much, while games like Diablo 3 or Dota 2 (named a few I recently played) do. At the same time, Diablo 3 doesn't suffer from input lag at all, and I too highly recommend playing it with vsync=on.
Those "few ms" are, in other hand, a huge disadvantage in games like quakelive.
OK, so sure - in a really, REALLY competitive arena, I'd probably suffer through screen tearing to be a few ms ahead of the competition. That's not really the argument, though, right? For 99.9% of people, who are not playing competitively, screen tearing is downright abusive on the eyes.
I just fired up Call of Duty Black Ops 2, with and without vsync, and with vsync+triple buffering.
These are my results:
I'm very sensitive to input lag, as I mentioned. Vsync off = great. Really responsive, no issues. Vsync on = holy crap horrible (with the bearing in mind that most people wouldn't notice. Of course, that's maybe irrelevant since most people are clueless to a/v or input lag anyway). Vsync on + triple buffering = ALMOST (and I do say almost) as good as with vsync off, but without screen tearing.
Honestly, I'd almost be willing to bet that even a "pro" gamer would have a hard time telling the difference between the vsync off and vsync on + triple buffering.
Now, I can't speak for all GAMES, but any games I own (about 400 Steam titles) have never given me an issue in terms of input lag.
But, again, this is subjective. I can't imagine anyone who games on an iMac (after all, we're not serious gamers, right? ) being upset with vsync+triple buffering.
And you're absolutely right about Diablo 3. The screen tearing in that with vsync off is just unfreakingbelievable.