Other mistake: When Deeds is rescuing Miss Keeling's cats, there are two mistakes. There are smoke and flames inside her apartment - both of them should be coughing a lot from the smoke. Oxygen gets displaced in a fire. Second mistake is why isn't any of the fireman inside the building coming up to her apartment or even fighting the fire? There is no way any fire dept or police dept is going to let bystanders just walk up to the scene as Deeds and Pam did.
Revealing mistake: Somebody has already pointed out that the footage of Deeds throwing the cats out of the window is obviously not caught on Pam's camera. In addition, notice that there is no guttering/pole to the left of Mrs. Keeling's flat window - it is on the right. Yet on the TV footage, there is a metal pole to the left of her window. Another point is that Mrs. Keeling's flat is on the corner of a street, yet when we see footage of the cats flying out of the window, her flat isn't at the corner of a street, it's in the centre of a row of flats. (00:48:55 - 00:51:45)
Revealing mistake: When Jan and Pam are fighting, you can tell for most of the stunts Winona Ryder isn't doing them, and it's a double. For instance when she runs into Jan, and gets knocked to the floor, and when she gets thrown into a table. This is confirmed on the commentary too. (01:10:50)
Audio problem: In Winchestertonfieldville, Iowa, Deeds and Pam find the house with blue shutters and a red door, that Pam had made up. When Pam pretends to show Deeds around she says "This is the dining room, where we would have our meals ... made of food." But Pam's lips don't move at all when she says 'made of food.' (00:59:15)
Continuity mistake: When Pam and Deeds kiss outside Pam's apartment, Pam has her right arm around Deeds and her left arm around him too, about halfway down his back. When the shot changes though, Pam is holding Deeds differently. Her right arm is no longer around him, and her left arm is up around his neck. (01:02:05)
Continuity mistake: When Deeds reads a card to everybody in the pizza shop towards the beginning of the movie, his last line, "...even when your bosoms sag down to the floor" causes one of the higher-aged men to cry. However, watch carefully: Deeds reads it, and everyone - including the man - laughs aloud. The very next shot shows him up close and wiping tears from his eyes, a smile being a far cry from on his face.
Other mistake: Just before Deeds enters the room where he punches the quarterback, you see Chuck Cedar talking to all his associates. While speaking to them he is speaking in perfect English and they all seem to understand. When Deeds punches the quarterback Chuck has to explain to some people in French as if they didn't speak English.