When Igby checks in to the O'Hare Hilton, the desk manager takes his credit card but never returns it, yet in the next shot it's back in front of Igby.
When Oliver comes into the loft and finds Igby and Sookie sleeping side by side, Sookie sits up slightly and the camera makes a quick cut to Oliver. The camera quickly cuts back to Sookie and Igby, and Sookie's head is back on the pillow again (as in the first shot) and then she sits up again.
When Sookie meets Igby in the street and invites him to the park, it's very overcast and looks like it's starting to snow. When they're in the park in the next scene, it's much brighter, almost sunny, and there's no snow.
In the opening scene, Ollie says at one point, "It's almost six." The scene takes place in the fall, so by then it would be dark outside, but it's as light as earlier in the afternoon in the same scene.
Rachel takes Igby's glass away after he spits back the sip he has just taken. In the next shot Igby is holding the glass, but the cigarette has gone.
When Igby is outside Sookie's door asking her to leave with him, the side of the door Sookie is on has a peephole, yet the side Igby is on is smooth and clearly does not have a peephole.
Despite talk throughout the film of a passage of time, the coming of summer, the advent of fall, and the approach of Christmas, the entire film was clearly shot over a very short time in the fall. In the scene outside the campus where DH tells Igby his mother is having a mastectomy, for example, DH talks about staying with him "this summer," yet there are dead leaves on the ground and bare trees.
When Ollie leaves Igby, Igby says "Say hello to Sookie for me" on the soundtrack, but his mouth is saying something else.
When Sookie enters the loft for the first time, she doesn't close the door all the way, and the door dramatically swings open, and then is shut by and unseen crewperson.