Continuity mistake: Near the end of the movie, when the band is about to perform in the stadium Josie is explaining some moralistic issues. When she's in a long shot her hands are at her side, and when it's a close up her hands are on the guitar. This happens as they cut between shots several times.
Continuity mistake: When the Pussycats first record music on the Megasound, they first sing and only Josie sings. When it's played backed, you can hear the backup vocals, even though there is no way they could have added it in, since Val and Mel hadn't even recorded themselves singing yet!
Continuity mistake: In the first scene, where DuJour are in in their plane, the pilot and Wyatt stand up out of their seats and prepare to jump. The camera cuts away, and when it comes back they are in different positions to jump than they were before.
Factual error: In the final scene where the band are playing, the stage contains several amps, yet none of them are wired up to any instruments.