(at around 1h 24 mins) As Dave's car drives away with the Chipmunks getting to drive, beep the horn and work the wipers, the sound for the wipers can be heard, but the wipers aren't visible through the windows.
(at around 56 mins) During the premiere party Simon says if he continues to eat he will go into insulin shock. Insulin shock occurs when a diabetic does not eat for an extended period of time. Given that there is never any other indication that Simon is diabetic (in fact he'd never survive in the wild if he was), he probably said it simply because it "sounds cool", without really understanding what he was saying.
(at around 1h 4 mins) Ian says the Chipmunks are going on a tour "coast to coast in 5 days". However, the schedule shown during the montage shows at least six cities, starting with Los Angeles, CA - July 4th, and ending with Austin, TX - July 28th.
(at around 38 mins) After Dave loses his job he writes a letter explaining that things aren't working out, and prepares a box for the chipmunks. He closes the box and pokes five random holes in the top. Moments later he changes his mind, and goes to the closet to put the box away on a high shelf. As he lifts it, you can clearly see seven neatly spaced holes.
(at around 11 mins) In the kitchen cupboard scene, Theodore chews a large hole in a box of Lucky Charms and eats some of the cereal. Seconds later Alvin dumps the bag of cheese balls on Theodore and the Lucky Charms box can be seen again without a hole chewed in it.
(at around 23 mins) The morning Dave gets up and finds the chipmunks making toaster waffles, he finds a stack under the rug. He picks them up and they are drenched in syrup. From there he goes to sing his song and never washes his hands but his hands are clean when he starts playing the piano.
(at around 10 mins) When Dave throws the basket of muffins in the metal trash can, one of the trash can handles is clearly visible as the camera zooms out. Moments later the camera zooms back in on the trash can and the handle cannot be seen.
(at around 11 mins) When Dave is lying on the couch watching television, two large jars can be seen on the counter top behind him. When he gets up moments later to investigate the noises in the kitchen, the jar with the white lid is no longer there.
(at around 3 mins) When Dave is late for work and almost forgets his pants, his old Pro Stereo skateboard is against the wall to the left of the front door. When he returns from his meeting, the board is to the right of the door and leaning in the corner.
(at around 1h 20 mins) When Ian lowers the curtain during the concert he pulls the rope down. This curtain system actually requires the operator to push the rope upwards to lower the curtain (counterweight system).
(at around 54 mins) When Claire is taking pictures of the Chipmunks at the party you can see a flash go off directly at them, even though Claire's camera doesn't have a flash attached. However, the Chipmunks are being flashed at every few seconds throughout the scene, even before Claire comes to their table, and after she leaves as well. It's obvious that all those flashes come from the other cameras nearby, not from Claire's.
(at around 11 mins) When Alvin opens the cupboard, there is a bag of Utz brand cheese balls. Utz brand is only distributed on the east coast. However, many specialty stores in California carry Utz items that they special order and have shipped.
(at around 33 mins) When Dave runs out of his home to get dinner for his date with Claire the time is 6:30 pm but it is still daylight. The movie occurs shortly before Christmas and at that time of year it would be dark at 6:30 pm.
(at around 23 mins) Dave takes the glasses from a Santa doll and puts them on Simon. It is unlikely that a Santa doll's glasses would have prescription lenses, much less prescription lenses that are the exact prescription Simon's eyes need.