Continuity mistake: In the scene where they're in the air close to the end of the movie, when Margo tries to jump to Gru's plane, Vector grabs her and points the squid launcher at Gru, then the moon hits Vector, knocking him and Margo off his ship. When Vector climbs back up to his ship, the moon's gone. It couldn't have rolled away because Vector's ship didn't move in that short time.
Plot hole: When Gru and his minions step out of the vault with the shrink ray he notices Vector walking by. Even if they managed to get inside the air duct before being seen by Vector in those few short seconds they didn't have the time to close the vault door as well without being noticed.
Factual error: The Times Square Jumbotron has a ticker-tape message beneath it. Some of the letters have sections missing, presumably to represent broken bulbs. If this is the case, the missing parts would not scroll with the message, as it's only the constant switching on and off of the bulbs that gives the impression of movement.
Continuity mistake: At the very end of the movie the 3 girls are performing on stage. Agnes is wearing white tights, but after the platform raises them all above the house she no longer has tights, just bare legs.
Continuity mistake: When Gru is hit by all of the missiles and guns that pop out of Vector's fortress he is standing right outside the large door, but in the next shot after he emerges from the crater he is in the middle of the street.
Plot hole: If the effects of the shrink ray wear off depending on the size of whatever is shrunk then the moon should have returned to its normal size within seconds of being shrunk.
Continuity mistake: In the very first shot of inside the orphanage, the tape mark on the floor is at least 3 feet away from the desk. The three girls stand behind it and 2 shots later we can see they are standing about an inch away from the desk. Then when Miss Hattie stands up, the tape is now a foot away from the table.
Continuity mistake: Justin, the boy with the toy aircraft running away from his mother, towards the pyramid in the beginning of the movie, has the toy in his left hand while going up the ramp, while falling and as he begins traveling up through the air but when the angle of view changes it is in his right hand until he lands on his father.
Continuity mistake: When Gru gets shot with all those guns at the end of his attempts to get in Vector's house before he first sees the girls, his goggles are at the top of his head. After he gets shot, the dust is not over his eyes, indicating that his goggles were over his eyes, shielding them from the dust.