Revealing mistake: You can see Buddy and Finch's stunt doubles in the ice skating scene. And when they are showing a close up of them you can tell that they are not really ice skating, but just doing the ice skating movement.
Continuity mistake: When Steve Finch crosses the street to talk to Buddy Hall outside the hardware store, he raises his collar around his neck. Slightly further on in the scene, when the two are in front of the tree, he places his hands in his pockets. The two then walk back to Hall's pickup, at which point Finch's collar is down, and returns to being up when they finish walking. At no time does Finch remove his hands from his pockets.
Plot hole: Buddy discovers a website, myearth.sat. The site, like Google Earth, contains satellite images of every square inch of the planet. Buddy can see his neighbor's house but not his own house. He decides to cover his house with lights so it can be "seen from space." There is absolutely no reason why the site would show every house in the world except Buddy's, except that the oversight is required in order to advance the plot.
Audio problem: You can tell that Tia is lip syncing in the final song ("Oh holy night") more so on the last few lines she closes her mouth before the song ends.
Continuity mistake: When Finch sneaks into Buddy's yard to unhook the lights, he jumps into the stall with the camel. At this time the camel vomits on his face. But when he gets out of the stall, his face is completely clear. One can argue that he wiped it, but there is no way he could have gotten it completely clean with just his hand. He did not have time for all of that.
Other mistake: When Buddy reaches inside the fuse box, after Finch puts snow in it. They cut right from him pulling it out to show his hands and there is a snowball in his hands. We do not see a snowball in the fuse box and he does not have time to shape one.
Continuity mistake: When Buddy is buying lights at the hardware Finch comes across the street to stop him. When someone comes over for Buddy's advice watch the shopping cart the amount of lights change from one (1) box to zero (0) boxes then when Buddy comes back to the cart there are two (2) boxes of lights in the cart.
Continuity mistake: In the scene where Buddy steps on the Christmas light and gets the idea of being seen from space, the path to the trash is clear of snow but when we see a shot of Buddy from above, the path is not cleared of snow, then it is cleared again.
Factual error: Although "Myearth" is a fictional site for the movie, all satellite sites (such as Google earth, etc.) show images during daylight hours (though I've seen rare exceptions of images during twilight hours). How could Buddy expect to not see his house (with or without lights) when the images show during the day?
Factual error: At the end when they show the lights shining in space from the satellite it is shining from the center of the map. The entire time they said it was set in Massachusetts, which would mean that it should shine from the right side of the United States coast.
Continuity mistake: When Steve's wife is getting ready to leave near the end of the movie, the driver's side window is down as she opens the door. As the camera shows her inside the car in the next shot, the window is fully up.