In the very beginning when the two criminals are escaping, there's an aerial shot of the getaway car. In this shot, we see that there are no cars in the vicinity of the car. A few seconds later when we see a shot inside of the car, we can see through the rear window that there are many cars surrounding the car.
The smudge on Jenny's face during the restaurant scene changes shape between shots.
The length of Hannah's skirt changes between the close-up and the far shot of when Matt is staring at her bottom while she is standing on that step ladder. The length changes again to shorter when she descends from the step ladder.
When Bedlam's bodyguard gets shot with cutting disk, in one shot it's pointing to the left. In the next shot it's pointing in the other direction.
Hannah takes Matt to her apartment for the first time. With her right hand she pushes him into a chair. Change camera and her left hand completes the push.
Sharks cannot walk or propel themselves on their pectoral fins while out of the water.
When the title appears at the beginning, G-Girl is flying at low altitude at high speed, but the trees nearby do not show any obvious movement.
After G-Girl's tornado tears off Matt's clothes in the boardroom meeting, the rear shots of him are visibly more muscular - obviously a body double.
At the beginning of the movie, when G-Girl foils the robbery getaway and the crooks shoot at her, the bullets supposedly bounce off her body and fall to the sidewalk. Actually, the bullets have clearly never been shot and are not even deformed, as they would have been if they had bounced off her. Also, if the bullets had ricocheted off her as they are supposed to have done, they would not fall in a neat pile at her feet.
During the scene where Jenny is painting her toes it switches from her foot double to her real feet when she lifts her feet up and the cotton on her toes fly off.
As the film opens, there's a shot from the back seat of the escape car looking forward. If you look at the dashboard, you can see the transmission gear selector is in park, even though the car's moving.
When Jenny Johnson/G-Girl stops the taxi with her super breath, actor John Cenatiempo comes out of that taxi to inspect his vehicle but in the next scene a totally different actor with glasses is driving that same taxi.
When Matt is trying to tell Jenny he wants to break up with her, and she stabs the cutting board with a knife, the knife makes a shuddering "twang" sound, which is impossible because she is still gripping the handle of the knife.
In the shark scene, you can see the legs of the shark operator and just after that you can see the camera reflected in the window.
In Matt's apartment, when Professor Bedlam comes to visit him, the Professor sits down on the couch and the reflection in the window shows someone walking in the reflection.
When Matt goes to Bedlams house in the cab, for some reason there a checkbook on the front of the hood.
In the flashback in which we see the meteor land, the trajectory of the meteor implies a landing point many miles into western New Jersey (the Manhattan skyline is visible in the same shot). Barry and Jenny, on the eastern shore of New Jersey, are the first people to reach the meteor, which is absurd.
In the early scene during which Matt and Vaughn are discussing the super power Vaughn would most like to have, they are clearly on a yellow-line R subway train. This is confirmed a short time later, when Matt chases a robber out of the train and they run up a staircase that says "uptown N R W". When they run out of the station, however, they run out of the red-line Franklin Street 1 train station. This is impossible, as the 1 train does not intersect with the R train, or any other train line, at this stop.
Matt and Vaughn were playing racquetball on a squash court.