The end credits list the family name for Don and Reese as being "Holden," however, on the title/cover page for "Golf," the new manuscript for the book by Don, the name is typed as "Holdin." Also, on the cover of the book which Don sent to Reese on her opening night the author's name is spelled "Holdin."
When Reese goes in to talk to Don when he's typing, right before she says something he pushes the typewriter back for a new line. After they finish talking, he pushes the typewriter back for a new line again.
Right after Reese kisses Corbit and he falls into the chair, his right-handed guitar is positioned correctly for left-handed playing. When the camera cuts back, the guitar is flipped and the strap passes over the neck of the guitar; putting it in an impossible position for left-handed playing.
When Reese first slams her hand in the drawer she clearly hits her fingers at their base. When she has lunch with Deirdre and her bruise is revealed, it's on the top of her hand.
In the movie, their car has a front license plate. Cars don't have front license plates in Michigan.
During the first scene that takes place in Reese's apartment, after she slams her hand in the drawer you can see a guy holding a light up in the mirror beside the big window.
In the scene in which Zooey Deschanel is having missionary sex, the gaffer tape over her nipples can be seen.
Taking the bus from New York to Detroit it was said that they had stopped in Traverse City. Traverse City is no where near the route they would of taken.