When Nick and Dan are talking in Dan's office at the beginning of the movie (when Nick is expecting to get promoted) Dan says, "You know I'm not good at making speeches, especially when I don't have you to write them for me." His lips don't match what he says.
When Nick thinks he's in line for a promotion to creative director, he and his staff make numerous references to moving up to the 44th floor. Immediately prior, there is an exterior shot of their building that is no more than 15 stories.
When Nick Marshall thinks he is going crazy and consults with his therapist, we see him enter the counseling office. The plaque on the door indicates that the therapist (Bette Midler) is a MA with a MFCC emphasis. He refers to her as Dr. Perkins. However, master's level therapists are not legally called doctors. They are known as psychotherapists. The only doctors who can conduct therapy are Ph.Ds, Psy.Ds, and MDs.
Just as Darcy and Nick begin dancing in the bedroom of her new apartment, some padding or floor protection can be seen covering the floor along the wall where she says her bed will go (covering the inlaid parquet of the floor). Moments later, as they are still dancing, the covering is gone (rolled up in a corner).
When Nick is standing in the middle of the department store, the long shot shows that the tiles on the ground under Nick's feet are the same light color as the rest of the floor. In the overhead shot, Nick is shown standing in the middle of a large dark colored star-shaped tile feature. The star-shaped tile feature is not visible in the long shot.
When Nick is in the psychiatrist's office the doctor is holding a pen in her right hand and is also holding the phone in the same hand. Then Nick tells her to guess a number and she does, and he repeats it back to her and she is amazed and hangs up the phone and throws the pen down on the floor. She then grabs the arm of the chair with the now empty hand. In the very next shot she has the pen in her hand again and throws it down again.
Nick and Darcy are discussing the sketches of the runner for the Nike project. Nick is making notes as Darcy is holding the ad workup card straight out in front of her. She hugs the card to her chest then with one hand, drops it to her side and in the next shot she has it back up in front of her, holding it with both hands again.
After being given the pink box assignment, Nick is watching TV. He turns off the TV and pours more wine, using his left hand to pour (across his body). Moments later the scene is shown from behind Nick, and he is putting the wine down with his right hand.
When Nick is trying on the pantyhose, he puts TWO runs/ladders in the left leg (one on the inner calf and one on the outer calf). Later when talking to his daughter & her boyfriend there are no holes showing.
When Nick walks into the middle of a department store and becomes overwhelmed with all of the thoughts he hears at one time, during an overhead shot the shadow of the crane used is visible on the displays besides him.
When Nick is trying to reverse the curse. He steps out to his apartment balcony and in the shot you can see he's in the shadow of the Hancock Building, but in the morning when he leaves his building, in the background you can see a sign for the street 'Fullerton Pkwy' which is over two miles away from the Hancock Building.
When Nick is going to Erin's house (the file girl) he goes out into the rain and stands in the rain and stays completely dry and then he gets out of the cab and his coat is wet but his face and hair are dry.
When Darcy is showing Nick her apartment for the first time, it's night time, and dark inside. She turns on the lights and shows him the living room, then goes over to the dining room, reaches in and turns on the lights there. Before she does, there is what appears to be street light shining through the windows on the wall. This light disappears an instant before the room lights come on.
Early in the film, when Nick returns to his office and the girls open the champagne, liquid can be seen coming out the end of the bottle before the cork exits. There was no cork in the bottle, just one already in Nick's hand. (This gag is revealed in the director's commentary.)