Visible crew/equipment: After Matt finds out that Nicole is engaged, he goes running through the streets. When he goes running past a glassed store display, you can see the reflection of a white van with the sliding passenger door open and a cameraman.
Continuity mistake: In the scene where Josh Hartnett is about to break his vow in the bathroom, he opens the window and jumps out. In the shot of people looking at Jerry, the window is closed when no one touches it.
Continuity mistake: Josh Hartnett is running through San Fransisco after he has found out his ex has gotten engaged. If you look closely you can see that his hair changes length.
Factual error: Josh Hartnett's roommate is reading the paper, which shows results from a big football game. But this movie is set during Lent, months away from football season. (The filmmakers admit this error during the DVD commentary.).
Continuity mistake: Toward the end, Josh Hartnett is handcuffed to the headboard and then has a dream. When he wakes with a start, his hands are free. But then he's cuffed again when he tries to leave the room attached to the headboard.
Continuity mistake: Toward the end of the scene where Josh Hartnett nearly drank the juice spiked with Viagara, Griffin Dunn is standing by the table and takes a drink of the juice, then sets the glass on the table. Just before the scene cuts to a different camera angle, his hand is empty, yet in the new camera angle, the glass is in his hand again and he sets it down on the table again.