Revealing mistake: When James Bond and Felix have found the missing plane, look at the colour of the water as the helicopter lands, it is evident that is landing in shallow water, (they are supposed to be in much deeper water with sharks swimming below them) you can see the sand below. If the helicopter had landed on deeper water, the water colour would be dark blue.
Revealing mistake: When the plane being piloted by the traitor crashes into the water, during the time while it's skidding across the surface and especially when it stops, you can see a large black wire attached to the middle of it and going into the "sky". (00:29:20)
Revealing mistake: During the fight at the beginning of the film, if watch it slow motion, you can see that the poker that is being used to strike Bond is not made of metal, it bends when the blows are being aimed at Bond. (00:03:10)
Revealing mistake: When James Bond and Felix go out in the helicopter for the second time to search for the mising plane, at the moment when Bond is looking through the pair of binoculars, and when Felix says "you won't find it down there, that's the Golden grotto" just look how slowly the rotor blades are turning, at this speed there is no way that the helicopter could possibly fly and besides, there is hardly any noise from the engine.
Revealing mistake: When Bond is wounded and on the run from Fiona and her assassins, he tries to lose them in a parade. At one point during the chase, for several seconds, there is a dog in the frame. Even without slowing down the film one can see that the dog is stuffed.
Revealing mistake: When the water jets are turned on in the DB5 you can see the fire hoses attached to the car providing the water.
Revealing mistake: When Largo escapes to Disco Volante, he closes the underwater hatch before Bond arrives. But the hatch can't close completely. A hole is visible (and light from behind). The hatch is obviously created in a studio, because the boat would not be able to sail - at least not that fast - with such an opening in the bottom.
Revealing mistake: Near the end of the film, when the bombs are on board the mini-sub, Bond is spotted by Largo and swims away, but is chased by one of the other divers who has a fight with Bond: Just before they get to grips with one another, you can see that the jacket of Bond's underwater suit is already torn at the right shoulder.