When Nick puts on the Panty-Hose, he makes a very large ladder in the left leg. Later there is only a small hole near the ankle.
Darcy's hair changes constantly between long shots and close ups in her speech in the first meeting she has with the staff.
Darcy eats her martini garnish of 3 olives on a plastic pick all at once. Then a few minutes later she does it again.
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 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.
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.)
Nick has a laptop with shining Apple logo on the lid. The logo is upside down and when camera shows the display it is Microsoft Windows and Microsoft Word on it.
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.
A fold can be seen in the sky between two buildings on the cityscape backdrop outside of Nick's window during the first scene in his apartment.
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.
Grammar mistake:
At 1:05:54, Darcy (Helen Hunt) holds a mock-up for an ad and is showing it to her boss. The line is "Livin' it to it's fullest." It should read, "Livin' life to its fullest," not "it's".
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 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 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.