The only reason I look both ways on a one-way street in NYC is because I've almost been hit by cyclists going the wrong way on a few occasions (and then been yelled at by that cyclist for not looking).

As an everyday commuter in Boston, I'm definitely guilty of not stopping at stop signs that I bike through everyday and not stopping when there is a pedestrian in the crosswalk (usually trying to get as far away as possible from them), but whenever I have to go down the wrong way of a one way street (Charlestown has is a bit confusing and it happens whenever I'm there) I go slow and sometimes even dismount.