Character mistake: Bruce Wayne talking to Selina Kyle says that Batman probably saved millions of dollars in property damage alone. When Batman first saw Catwoman he didn't do anything to prevent the property damage before the explosion that she caused.
Character mistake: At the very end of the movie, Jack Lemmon begins dealing cards for the gin rummy, but he deals about 14 cards before the fade to black, in a 10 cards game. (01:59:45)
Character mistake: In every scene George is with Mary, she never once wears glasses. However, when he meets her coming from the library after he was never born, she is wearing glasses. George is shown how he has influenced all the people in Bedford Falls over his lifetime, but having Mary's eyesight degrade to the point of needing glasses isn't one of them.