Other mistake: In the last shot of the film, the zombies are walking across the bridge to New York City. Below, there are cars on both sides of the bridge driving to and from the island with absolutely no concern for the chaos that is supposedly taking place. I guess the filmmakers couldn't stop traffic for a few minutes to get the shot?
Revealing mistake: When Dr. Menard is driving and discussing the zombie plague with the visitors, the "clean" part of the jeep's windshield (i.e. the path of the windshield wipers) appears to be cut out of the glass (probably to provide a better view of the actors and prevent the camera being reflected on the glass).