Continuity mistake: When the guys are looking at Andie's purse on Ben's desk, the two handles are sticking straight up but the close up shot shows the front handle folded over, and then the next wide shot shows them both up again.
Continuity mistake: In the scene where Ben just ran down the fire escape to Andie, she walks away waving. In the shot of her front side she's waving with her right hand, and then in the next shot (a rear shot) she has her left hand up.
Continuity mistake: In the scene where Andie and Ben are riding the motorcycle and she is wearing a white tank top, you can see the outline of her bra. When they go back to his parents' house and Ben takes off Andie's tank top in the bathroom, she doesn't have a bra on.