Continuity mistake: When Nick is singing "Spend This Night with Me", he brings up a girl from the audience. Watch the background. When it shows another girl from the audience, in the next shot, you can see a speaker that wasn't there before. Moreover, when he picks the girl, we can see that there isn't anyone at her left side. But a few seconds earlier she was sitting between two girls (the one at her left was wearing a white shirt). (00:42:05)
Continuity mistake: When the Rad Pack first meets and are skiing together, Dan O'Callahan is wearing a blue baseball cap and sunglasses. In some later shots he is wearing a stocking cap and goggles. (00:31:25 - 00:32:00)
Continuity mistake: When Ariel and Rusty are at the diner discussing Ren, Ariel has a French fry in her hand halfway up to her mouth, but when the shot changes her hands are back to the bowl of fries. The bowl of fries move closer to her between shots as well.
Revealing mistake: When Hanks drives through the city escaping form the MPs, the guy driving is a very obvious stuntman.
Continuity mistake: When Elaine gets knocked out with the ball her hat falls to the ground, next to her car. When the boy drives off the hat is gone. (00:12:55)
Continuity mistake: The note Jenny puts up in the restroom changes; when Starman goes into the bathroom while Jenny is signing the receipt, notice that the postage stamps holding the note to the mirror are now in different positions and the word "help" is smaller. (00:35:55 - 00:36:45)