Revealing mistake: When David is sitting in L.E. at the end and the camera is zooming in on his face his mask changes. In the very last shot of him just about to pull it off it's much wider/looser so it'll come off easier.
Revealing mistake: During the love scene towards the end of the film, with David and Julie, it is obvious that Cameron Diaz (who played Julie) is only in the bed for her shots. The reverse angle of David shows him making love, but other than a badly-matched wig on the pillow there is nothing to stand in for Diaz. There is no sight of her body or head, and the wig is the wrong color and shape, not to mention it looks like a wig.
Revealing mistake: The office of LE is located in the California Gas Tower, an office building in downtown Los Angeles. The movie is set in New York City.