Revealing mistake: In the scene when Pacino leaves the police station to go to his hotel for a shower, the camera is pointing up a tree lined street. Watch the pedestrians - they are all standing still until the car comes into view then someone obviously shouts action and they all start walking.
Revealing mistake: When Neil & Co. are in the restaurant after the armoured car robbery, they all get up to leave to deal with Waingrow. The next shot is from the parking lot of them leaving the restaurant. Right as the shots switch, they are all standing still lined up at the door for a second, and then they start to move out the door (once the director yelled "Action" I'm sure).