Continuity mistake: When Madison is speeding away in her Shelby Cobra with the Angels hanging on, she crashes into a theatre. While in the theatre, there are shots of the car in the background. It is a completely different car than the Shelby that Madison was driving a few minutes before. The racing stripes are thicker, the wheels are different and the car is actually a lot bigger.
Continuity mistake: When Demi Moore shoots the Angels off the side of the observatory, the bullet intended for Drew Barrymore hits her in the lower abdomen. Later in the movie when the Angels wake up on the lawn below the observatory, the only bullet hole in Drew's shirt is on her upper left chest.
Factual error: Helicopter rotor blades do not unfold by themselves and there is no way to unfold them from inside the helicopter. A trained mechanic with the right tools and equipment (including the proper ladder for the job) will take a minimum of twenty minutes to rig a four bladed rotor, and that's if (s)he's in a hurry. An airborne (i.e. falling) helicopter? Forget it.
Deliberate mistake: Bosley is a school crossing guard trying to help the Angels. The children behind them say they are gonna be late for school. Of course they're going to be late because there is not a school within 10 miles of where they are standing. There's trees and what looks like a huge mountainside on the other side of the street. You can see this more visibly as the car that is about to run over Bosley is approaching. Done for a gag, but still ridiculous.
Continuity mistake: When Natalie is talking to the surfer by his car, Alex and Dylan are under the car looking through his belongings. After he gets into the car to drive off, it cuts to Natalie and she says something, cuts back to the surfer pulling away in his car and then cuts to a shot of Dylan but you can see the surfer's leg/towel in the shot. Shouldn't he already be in the car?