Revealing mistake: In the scene where Reese Witherspoon is entering the elevator after being harassed by her mentor, you can see Selma Blair's reflection in the plaque right before her cue. You see her reflection right before the doors close, so you know she was waiting for the cue.
Continuity mistake: When Elle is at the beauty salon she has 2 flowers in her hair, one purple, and one pink. When the camera angle changes, the flowers also change position from shot to shot.
Continuity mistake: When Reese Witherspoon is eating chocolates after being dumped, look closely at the box. When she finds one that she likes, there are two white ones one row in from the back. Two seconds later, just before she throws the box at the screen, there's only one white one, and it's moved forwards a row.