Factual error: In the final standoff, Smith shoots Hertz by holding cartridges between his fingers in the fire. This is not remotely believable. The casings, weighing much less than the bullets, would have been blasted off while the bullets themselves would have gone nowhere.
Deliberate mistake: After Mr. Smith terminates the plethora of skydiving shooters, they all end up in an area the size of a basketball court, despite having markedly dissimilar velocities and trajectories created by the order in which they were shot.
Continuity mistake: During the love scene between Smith and Donna, when the killers first come in the door, Smith's pants keep changing from being down (while he is having sex with Donna) to up around his waist like normal as he rolls off of the bed.