Continuity mistake: In the airport scene Scott Caan introduces his new "girl" to Paul Walker and Jessica Alba. In the background behind Paul you see a long-haired brunette wearing a strapless shirt walk out of the terminal and continue past the camera. The shot changes to a wide angle of the four main characters, and a second or so after the change you see the same brunette come out of the terminal again.
Continuity mistake: When they are pulling the cannon onto the boat, about ten minutes prior to the end, there is no water on the cannon, it is completely dry though it just came out of the water.
Audio problem: Notice when anything heavy hits the bottom of the ocean it makes a loud thud. The bottom is soft sand and wouldn't make noise.
Plot hole: When the group first finds the plane, they are all able to hold their breath long enough to descend, search the plane and resurface. Yet later in the movie, even though Amanda can get a full breath of air from the air pocket in the plane, she can't hold her breath long enough to swim to the surface and has to be rescued by Jared.
Visible crew/equipment: During the scene where Paul is mad at Scott for not telling him he had no money to buy a boat, the mic wire is visible outside Paul's collar.
Continuity mistake: When they first discover the wreck and they are pulling pieces of treasure up to the rear deck of the boat, Jessica's fins change from the clear fins to a set of blue ones without her changing or getting out of the water.
Revealing mistake: When the guys are on the jet skis, when they are showing off, you can tell they are stunt doubles.
Visible crew/equipment: When Scott Caan's arm is caught under the cannon and Paul Walker lifts it to get him out, when the cannon is dropped back to the ocean bottom an air bubble floats to the surface. As the camera follows the air bubble a camera man in the water is visible on the right side of the screen next to the boat.
Continuity mistake: The scene where Paul Walker and Scott Cann are wrestling in the water when the sharks show up, Paul Walker is wearing a diver's mask when they start. Then it cuts to a different angle and he is not wearing it, and then asks Jessica Alba to throw him his mask when he surfaces.