Other mistake: Near the end of the movie, Greg says he's in row 8 on the plane. But when he's on the plane, we see there are only about 7 or 8 rows behind him. If the plane had only 15, 16 rows, the plane wouldn't have that middle section of seats.
Other mistake: When Greg asks the kid behind the counter if they have the Nicorette patches, he says no, and hands him a pack of the Nicorette gum. However, the package to the left of the gum, and possibly to the right, are patches.