I think, overall, that our perceptions regarding implants are skewed due to the fake breasts that us guys actually see. That is, those way-too-large and obvious fake boobies we see (or so I'm told ) on the young women in strip clubs, tabloid ads, and R-rated "skinimax" movies. If done well - and here in L.A. there are a lot that have been "done well" - you really don't notice the fake ones that much. They don't stand out - er, uh, you know what I mean - like notoriously fake porno boobs.
I think most women do know "when to stop." But it's the ones who don't who have the boobs that we actually get to see.
Or so Catesta tells me...