Pitbulls are great dogs. Unfortunately they get a bad rap because of irresponsible, heartless owners that raise them to be as vicious as possible, and often will intentionally breed aggressive genes into them so that the next generation will be even more vicious than the preceding one (for the purposes of dog-fighting). It's absolutely disgusting and gives what is a wonderful dog a poor reputation through no fault of its own.
Agreed... I usually can tell the ones that are harmless because they don't have cropped ears or tails. If someone does that to their Pitbull then they probably want them to look mean. That's not to say it's always true but I'm definitely more leery of Pittbulls with cropped ears.