Factual error: When John Cusack puts Springsteen on his LP-player, he places the needle at the start of the record. The song that plays is the studio version of "The River." Therefore, the album has to be "The River," which is a double album, but "The River" is not at the start of either of the two LPs, but is the last song on LP #1. (00:18:10)
Continuity mistake: When John Cusack is on the phone to Catherine Zeta Jones he enquires about her marital status. When she responds she is holding the phone in her left hand with a large ring on her ring finger. Cutting away and then back the phone is now in her right hand but the ring has jumped to the ring finger on that hand also. There is now no ring on her left hand. (01:08:15)
Factual error: When Rob visits Charlie, it's clear, from everything to her clothes to her home decor to the design of her loft, that Charlie is a wealthy person who lives in a fancy apartment. It's also clear that she's very snobby and shallow. Yet when Rob leaves from his evening at Charlie's, the address shown is in the middle of a very rundown and rather isolated neighborhood that in 2000 (when the film was made and set) was poor, somewhat crime-ridden, and years away from being anywhere someone like Charlie would have been caught dead in. Not only that, but the type of building is not to be found in that neighborhood anyway.
Continuity mistake: When Rob gets back to his apartment, when he places Marie deSalle's CD into his CD player, the second track reads "Patsy Cline Times Two," as it is called in the Nick Hornby novel. Much later on in the movie, when Rob meets Barry, Dick, and Marie for a drink, Marie comments, "You know that song I play, 'Earth Kitt Times Two?'" in response to Rob mentioning that he left his apartment to let Laura move out more of her stuff. (00:25:45 - 00:57:45)
Continuity mistake: For Chicagoan "L" riders: At one point in the film, John Cusack is riding the CTA, or the "L", train and speaking to the camera. He is shown walking up the steps to the platform to board the train. He boards a Purple train (you can tell from the banner in the window). After he is seated, out the window you can see the Graceland cemetery, which is north of the station in which he boarded the train, but because of where the cemetery is shown, the train can be determined to be heading south. The scene ends showing the train going underground to the subway. Purple L's do not switch to the underground tracks. So Cusack either magically transferred trains (if possible, I'd like to know how) or the L decided to change its route for unlucky John. (00:40:10 - 00:41:20)
Factual error: When Rob is going through the mail in the lobby of his apartment, he picks up an envelope which has an address listed like this: 12345 Street, Chicago, Illinois. (I forget the name of the street.) However, in Chicago, that mail would never have actually been delivered anywhere: all the street addresses within the city of Chicago are specified as to whether the street is North, South, East, or West - an address that didn't specify one of that would have just stayed in the dead letter box at the post office.