Continuity mistake: In the beginning of the movie when Rachel enters that bar and is welcomed with the surprise party, Darcy comes and puts a colorful necklace around Rachel's neck. In the next shot, Rachel doesn't have the necklace anymore and Darcy is putting it once again around Rachel's neck.
Continuity mistake: When Rachel and Dex are standing on the steps outside her apartment, in one shot from the front she puts her arms behind her back. We cut to a side shot and her arms are now by her sides.
Continuity mistake: In the scene where Rachel runs back to Dex and starts talking to him in front of the bar in the rain her damp hair changes positions (particularly around her face) between almost all of the shots.
Continuity mistake: In the scene where they are all at the beach about to play volleyball (and reveal secrets) Ethan opens a beer when he first sits down, then a minute later, without drinking quickly, he opens the cooler and gets another beer.
Continuity mistake: When Dex and Ethan are playing badminton, the sun changes between shots.