In the final archery scene, David removes all but one of his arrows from the target, then is distracted by someone asking for an autograph. In the following long shot, the final arrow has disappeared without David ever having removed it.
When Dave puts the new tag on his license plate, the first set of three numbers is separated from the second set of three numbers. But a moment later, a front shot of his car shows all six numbers in a row with no separation.
The parade scene at the very end is supposed to be taking place in New York, but if you look at the firefighters' uniforms and the emblem on the firetruck, they are clearly from the Chicago Fire Department.
David Spritz tells the audience that the archery range he takes his daughter to is in Bollingbrook when in fact it's actually located on Main Street in Plainfield. Furthermore, he notes how it's a 90min drive from Chicago. Both Plainfield and Bollingbrook are just under an hour or so away from Chicago depending on traffic via i-355 or i-55 expressway. Lastly, he tells his daughter "we can go UP to the archery". Being in downtown Chicago when he says it, Bollingbrook is southwest of Chicago. He should have said "down"
When Dave buys the coffee in the Arby's, the total goes from $.72 to $.80. That would place the sales tax somewhere between 10.4% & 11.7%. No state, including Illinois where this movie takes place, has a sales tax that high on food.
If you freeze the scene immediately after Spritz deletes his book Breaking Point, you can see there is still a Word file on his desktop labeled Breaking Point, so he didn't actually completely delete it. However, when a file is deleted by one application, such as Word, other applications, such as Windows Explorer (what displays the desktop icons,) don't update instantly. Sometime it can take several seconds for the changes to be reflected in other programs. Also, the icon on the desktop could be a shortcut to the actual file in My Documents, in which case the icon will not disappear automatically. It would have to be deleted separately.