Continuity: When the heroes dedicate their boat, Demi Moore's character knocks a hole in the side of the boat. In subsequent shots, the hole looks like it's been partially repaired.
Factual error: When Ack Ack is collecting shells on the beach for his father, he's really collecting shell casings... which should be where the guns are fired, not where the explosions are.
Continuity: The horns on John Cusack's Viking helmet alternate between the front and back of the helmet in different shots - apparently, he had it on backwards for a while.
Visible crew/equipment: During the boat race when the rabid dolphin captures the man, the little girl raises out of the top. You can see a crew man inside the hole on the right of the girl.
Continuity: When Hoops is talking to Demi Moore's character on the beach and he draws her a picture of a gorilla, you can see the page is already drawn on before the animation scene takes place.