When Jason is checking out William Matherson's facebook page, even though Jason only learned about him a few seconds before, the "friend-box" shows that they are already facebook-friends.
When Ellie gets a call from Jason while sitting at her desk, the picture frame with the drawing he sent her is standing right in front of her. In the next shot the frame is gone.
When the three characters are drinking at the bar during the end of the movie, they number of beer bottles changes. First the waitress brings them a 4th and 5th bottle, in the next shot there are 4 bottles, then 3, then 4, then 3 again, then 4 for the rest of the shot.
When Daniel and Chelsea are in bed in her room, the position of the teddy bear shifts between being completely up against her pillow or between the bed and the nightstand, until the shot right before she moves the bear, when it is actually on the nightstand.
When Jason is on his way home from his date with Ellie he calls Mikey and ask if he is home. Mikey than ask how it went with the "hooker" and Jason goes onto explain. The next morning when Mikey comes home and burst into Jason's room he asked again "How did things go with the hooker?" But he already should have known from his phone conversation the night before, so there was no reason for him to bust into the bedroom.
In the bathroom, when Mikey tells the group that he was with Vera, two different men's voices can be heard when the group express their disbelief. But only Jason moves his lips while Daniel does not.
When Ellie shows up at Jason's apartment with "scotch," she is actually holding a bottle of Bulliet Rye Whiskey, not scotch.