Continuity mistake: In the scene where Buddy is singing along with Jovie (who is in the shower), it shows Jovie singing and her hair is obviously wet. However, when she stops singing because she hears Buddy, the shot cuts to Buddy on the counter, then back to her. Her hair is dry and stringy on the bottom. It is more obvious when she sticks her head out of the shower.
Continuity mistake: In the scene when Jovie is asking Buddy why he was in the girls locker room, the amount of people in the background changes each time it cuts back from Buddy to Jovie. It goes from originally five people to three, back to five and so on. This is obviously a mistake because the characters in the background are the same when it's five and the same when it's three.
Continuity mistake: When Emily is eating spaghetti, you can see she is only using a fork and there is a knife next to the plate. In the next shot the knife is now on the plate despite the fact she only uses the fork to eat throughout the scene (also there is no sauce on the knife so very doubtful she used it to help her eat the spaghetti). In the following shot of her the knife is back by the side of her plate again.
Continuity mistake: In the scene where Buddy's Dad is talking to his manager about the missing pages in the book, and how the manager thinks that the company will post a minus eight for the quarter and storms out of the room, Buddy's Dad's arm is resting on a piece of paper that is almost directly in the center of the table, and after it cuts to the manager and back to Buddy's Dad, the piece of paper is close to falling off the table.
Continuity mistake: The scene in James Caan's publishing conference room when Buddy and Myles Finch are wrestling results in Buddy's foot hitting the far left picture of three pictures on the wall. The picture comes crashing down and you hear breaking glass. The next shot reveals the fallen picture back up on the wall unbroken. It is followed by the next shot showing the picture gone off the wall again.
Continuity mistake: When Buddy has made breakfast for the family, Emily eats the spaghetti taking from the side of the plate and does not touch the top. When the camera goes back to the plate the spaghetti has been all stirred up with the sauce now mixed in, instead of just piled on top.
Revealing mistake: While we see Buddy drinking the entire bottle of Coke, it is quite obvious that he is not actually drinking it. Buddy has his lips firmly sealed around the end of the bottle and gulps down the entire lot. If he was drinking it, the bottle would have caved in as no air was getting inside. It was not even possible for him to blow air from his nose back into the bottle due to the fact that he is continuously gulping.
Visible crew/equipment: In the scene in Central Park when Santa's sleigh has crashed and Buddy is repairing the engine, the line that is holding the reindeer in place is visible on the lead reindeer. Not the harnesses that are around each reindeer but the line that is keeping the lead reindeer leashed to the ground is visible.
Revealing mistake: Towards the beginning, in one of the scenes where Buddy is sitting on Papa-Elf's lap, you can see Bob Newhart is not quite lined up with Buddy, or his legs in the foreground (Which are actually the legs of a little kid), as he is really a short distance away, to make it look as though he is shorter.