Continuity mistake: In the scene where Vince Vaughn is complaining to Harvey Keitel in Harvey's office about the hitman he hates his gold necklace is either tucked into his shirt and red tracksuit or hanging out. This alternates throughout shots but during the same conversation.
Factual error: A very common error in First World War films. British soldiers were not permitted to shave their upper lips until 1916 - in 1914 almost all (unless physically unable to grow them) would have had moustaches.
Factual error: The frozen treats used at certain points in this movie are labeled with nutrition labels found in the U.S. today. The labels looked extremely different in the 70's.
Continuity mistake: The white Mercedes has a sunroof in some shots, and not in others.
Factual error: Towards the beginning of the film, the Cashes receive a notice about their rent. It's the 1950's and the address has a ZIP code. ZIP codes were not introduced until 1963.
Continuity mistake: In the room when DJay first plays his keyboard, the dirt pattern on the door behind him changes drastically when the scene changes.
Continuity mistake: After Elvis's first live performance, his parents are discussing how proud they are. They and the crowd are still moving in time to his song even though he's already stopped, indicating the scene was originally intended to take place during the song.
Factual error: In the scene where Brian gets fired from The Rolling Stones, Keith Richards sees a live album Jimi Hendrix and mentions it, Brian says Hendrix sent him one. But this scene must have taken place in 1969: Hendrix hadn't released any live albums earlier than 1970.