Jack's friend has to get a triple bypass the day after the party, however he is seen at the bowling alley a short bit later in the movie, without enough days passing by to recover from such surgery, especially in the year 2000.
During the Christmas party, when Jack learns of Kate's profession, Kate eats an olive on the toothpick, however in the next shot of her the olive has reappeared, and in the shot after it is again gone.
Kate's hair style is different between shots when she knows Jack did not prepare anniversary gift for her.
When Jack is bowling with the team from Big Ed's he leaves a number of pins standing. When he turns aways from the lanes, feeling triumphant, we see that no pins standing and they're not being re-set.
Jack wakes up in his alternate life on Christmas Day. About 8 or 9 days later he begins a regular work day by taking his daughter to elementary school. This would take place in January after New Years Day, however when he arrives at work (Big Ed's Tires) the store is decorated for Christmas and playing Christmas music.
Jack Campbell said "We have a full day of market trading" on Dec 24th but the stock and bond markets always close early, stocks a half day & bonds one hour later.
When Jack wakes up the day after Christmas and sees Kate in the shower, she says "Tuesday's your day", implying it is Jack's turn to take the kids to winter camp and daycare. This means Christmas was on Monday and Christmas Eve was on Sunday. Jack was at the office on Christmas Eve and he told his employees in the war room there was still a full day of trading but the markets never trade on Sunday.
At the Christmas party, Jack's friend in the New Jersey Nets jacket asks the group of men, "Did you see Van Horn last night?" but the NBA never has games on Christmas Eve.
As Cash drives the Ferrari with Jack on the passenger seat, the tires are squealing. This would be impossible on an icy road, partially covered in snow.
The license plates on the minivan from New Jersey have a different typeset than real plates.
Jack and Kate used to live in the Village, yet Jack asks Annie if he had "ever taken her mother to the City". Since they moved out around the time of Annie's birth, this clearly refers to the time after that move.
When Jack sees Kate after the glimpse has ended (as she packs to move), she has a very distinct hair cut. Just a few hours later when Jack confronts her at the airport (and they eventually go for coffee), her cut is a completely different style, much more similar to Kate from the glimpse.
When Jack and Arnie are walking to Jack's house just after they met for the first time, there is a dog passing by in the background with visible guiding line, making him walk down predefined path.
Kate complains about Jack's potential commute from Teaneck to Wall Street. But, depending on traffic, it's as little as 20-30 minutes, as evidenced near the end of the film when Jack says he'll be in the office in 20 minutes.
At the end of the movie, when Jack is supposed to be going to JFK airport to stop Kate from leaving, the scenes from the airport are actually LaGuardia Airport.
During the bowling alley scene, Jack's friend says something about all the men in Union County liking Kate, except they live in Teaneck, which is in Bergen County.
Jack's apartment is in the Olympic Tower at 641 Fifth Avenue. His office is in the Seagram Building at 375 Park Avenue, just two blocks away (a six minute walk). Yet, he is shown driving his Ferrari through Central Park on his way to work.
After getting denied access to his apartment complex by Tony because he's not recognized, Jack drives to his office building. As he walks in through the revolving doors, Jack accidentally hits his head on the glass and ends up touching the spot that he bumped but continues with the scene.