bevinator: The eye can't really see much of a difference (or any difference) past around 35 fps, so the only real reason you need more than that is so when the game is rendering complex stuff onscreen, the standard rate won't drop below that. Unless the game is too advanced for my graphics card anyway, I generally leave it on for most games, because the fps drop is usually not noticeable in any way, but the screen tearing often IS noticeable. I have had a few games that looked worse with it on, though, so it's really game-dependent. I'd say I leave it on for about 70% of my games, with the other 30% being games that don't have noticeable tearing in the first place, or have major performance drops with it enabled.
I have to disagree with you and agree with Paradocks.
Try this if you still not convinced:
http://frames-per-second.appspot.com/
;)
I REALLY notice when fps is below 60 (55 is enough for me to notice)
I can't really notice tearing unless I'm looking for it.