Factual error: When they stop at the gas station to ask for directions, you can see a Country Style donuts sign on the outside wall. Country Style is a Canadian brand.
Revealing mistake: After they almost drive the Xtreme truck off of the cliff, Kumar gives a speech on their ancestors. He appears to be standing too far in front of the vehicle, which is partially over the cliff. In some shots in the same scene we see him standing on a short outcropping, but the angle of him to the vehicle doesn't match with the earlier shots.
Revealing mistake: In shots of the drive-through guy at the the Burger Shack, it can be seen that the restaurant has no back wall.
Factual error: Near the end of the movie where H&K are stealing the skateboarder's truck, there is a Shoppers Drug Mart in the background. Shoppers Drug Mart stores are only located in Canada, not New Jersey.
Continuity mistake: Harold's Toyota Camry changes between shots a few different times in the movie. In the beginning and for the majority of the movie, the Camry is one of the more expensive trim levels with alloy rims. During some of the shots, it switches back and forth from this to a base model Camry with wheel covers. One of the times this happens is when they are wrestling with the raccoon.
Continuity mistake: As we see Harold and Kumar in the car we see a close up shot of Harold on his laptop. We also see a USB wire in the side USB port to which is attached a small light set off to the left of the screen. In one of the wide shots this light can be seen, but in all the others it has disappeared.