Continuity mistake: At the wedding, Rory puts his arm on Sam's shoulder. When Sam is mid-sentence ("For better or worse"), Rory's arm disappears at the cut. (00:06:50)
Continuity mistake: In the scene where the mother and boss of the company is giving a speech, in one shot the puppy she is holding is resting on her shoulder; in the next shot it is lying in her arms, and then finally in the next shot it is back to resting on her shoulder.
Continuity mistake: Katherine Heigl's hair color changes quite often in the movie - it goes from fully blond to blond with slightly dark roots to visibly grown out dark roots in the same "day" (see when she is on the phone in the kitchen and when she slaps Jensen for the first time).
Continuity mistake: During the entire RV scene when Josh is going to NYC, it is obvious the 'living room' slide of the RV is extended. In the shots looking forward, the seat is well left of the driver's window.
Continuity mistake: When Lea Michelle is trapped in the elevator she is wearing black nail polish on short nails. When she performs her solo her nails are now painted white and are longer.
Continuity mistake: When Bon Jovi gets slapped, his two necklaces change positions (not from the slap, but when he is just standing still).
Revealing mistake: In the scene when they are travelling in the RV, the tea in the glass is perfectly still, even when the RV is obviously in motion. The tea should be jiggling in the glass.