Other mistake: During the sex tape scene, the blinds are closed to prevent someone outside from looking in. About 30 seconds later, you can see the blinds crinkle a little bit, to show the "hollow man" has split the blinds open in order to peek inside. This isn't possible to do from outside, as the window would be in the way.
Factual error: The guy who is invisible is ran down by a car while running after the cop and the scientist. He is shown getting up covered in blood. Everything about him is invisible which includes his blood. It shouldn't have been visible after the accident.