Pattern I've noticed in a variety of different online hold 'em games:

flop:
player 1 (UTG) bets around the size of the pot on the flop.
player 2 (later position) raises by the same amount.
player 1 calls.

turn:
player 1 checks.
player 2 bets hard.
player 1 folds.

Why does player 1 act like this? This pattern is numbingly predictable. If you're going to check/fold the turn, just fold the flop and save some money. Probably some of them (most of them?) are hoping for their hand to improve... well, how often does that happen? If you're lucky and on a strong draw, you have maybe a 1 in 5 shot. If you're a normal guy with a normal hand, like top pair/weak kicker, give up. No help is coming. The one time it does come just costs you money the other 10 times you make that flop call.