On IMDB, there is a link talking about goofs & mishaps with the movie.
Kristen Stewart's mike was clearly visible between the hem of her shirt and the waist of her pants when Charlie takes Bella to her bedroom in the beginning.
In the ballet scene, after Edward hits James, you can see blood coming off of his lip. But vampires do not have any body fluids other than venom.
Note: A lot of these are inaccurate.