Visible crew/equipment: When Peter is at the golf course with Mrs. Arness, you can see the golf cart in back of them. In the next scene, there is a woman sitting in it and she appears to be the stand in for Mrs. Arness. (Confirmed on the Audio Commentary)
Deliberate mistake: It is not believable that Charlene, the dangerous prison escapee, would seek legal assistance to re-open her case, and not be concerned about escape charges, in addition to freely being seen by many people.
Visible crew/equipment: When Peter is going home to get ready for his "date", he goes to get wine out of the fridge. If you slow down on the DVD you can see part of the camera and a man in a pink shirt standing next to the camera operator (director Adam Shankman?).
Continuity mistake: At the end of the movie in the scene where they are moving into the new office, Peter is talking to Charlene at his desk. Behind her there are three books stacked in a certain order. Later in the scene when he is talking to his wife the books are stacked differently.
Revealing mistake: During the fight scene between Charlene and the girl, as Charlene hits the woman it is visible that she does not even touch her.
Continuity mistake: When Mrs. Arness is playing golf the sun is casting a shadow behind her. After she hits the ball she turns 90 degrees and the shadow is still behind her when it should be beside her.
Continuity mistake: When Steve Martin and Queen Latifa are dancing at the club that his ex wife and her sister are eating at, when the ex wife and sister are talking the ex wife's bangs change from sideswept to centre.
Continuity mistake: When Steve Martin is trying on outfits before Charlene comes over, he puts a sweater on over a collared shirt. When he looks in the mirror, his collar is all messed up, but when he turns around, his collar is straight.
Continuity mistake: When Peter catches Georgey reading the adult magazine, Peter says to Charlene, "I'm turning you in." At this point in the movie Peter doesn't know she escaped, so there would be no reason to turn her in.