While Thom is explaining The Beatles song "I Want To Hold You Hand" he incorrectly says it was their first single. It is true that it was their first major-label United States single (presumably what Thom meant), but the Beatles released several earlier singles in the UK, and some of them were also issued in the US on minor labels.
When the "jerk-offs" finish their set at the beginning of the movie, Thom takes off his guitar. When Nick tries to turn off the drum machine, Thom comes over and kicks the plug out, still wearing his guitar.
When the cab pulls up to where the Yugo is parked and Tris gets out and slams the door on Gary, the door window is shown as rolled up. In the next frame when Tris blows off Gary, the window is shown as rolled down. In the next frame, panned back to Gary, the window is rolled up again.
When the convenience store owner is talking to Nora about having to chip the barf out of the ice cream cooler again, Tris pushes open the door and walk into the store, dropping her arm to her side. In the next shot, Tris is again seen with her hand on the door and again stepping into the store.
When the Queercore band members arrive at Nick's house they knock the trash cans over and a Tide detergent container spills out on the lawn. A scene later when they show the spilled trash there is a milk container next to the Tide container that was not there before.
When Norah is being chided by Tris in the convenience store (about never having a climax), the man behind them puts a bottle on the counter and rests his arm there. A split second later, his arm is hanging at his side and the bottle has vanished.
When Nick meets Norah at the diner, they have a conversation about Tal and Becka Wiener and more. The conversation switches from them sitting at the table and then walking down the street then back in the diner then back on the street. The conversation is fluid but the scenes are not.
When everyone finally finds "where's fluffy" (after the radio hint for 5th Avenue at 68th Street), and they are climbing to the roof of that address, the Empire State Building is shown towering above the rooftop and can be no more than a block or two away. In reality, the Empire State Building is more than 30 Blocks away from that address and would seem much more distant. The proximity of office buildings and their exit via Penn Station would lead one to believe that they were in the Midtown area likely between 8th avenue and 5th with and between 31st street and 35th - not the address mentioned on the radio hint.
At the end of the movie, Nick and Norah are entering Penn Station, presumably in order to get home. Nick lives in Hoboken, and could presumably take the PATH train from 33rd St to Hoboken. But there is no access from Penn Station. Norah lives in Englewood, and there is no train access there, so Penn Station would not help her. She would more likely take a bus from Port Authority Bus Terminal (where they had been earlier in the night).
During the opening credits montage, we see Nick driving into New York city. We see his car come around a curve and the camera pans up slightly, showing a view of Midtown, implying he is driving into the city. The road he was driving on was actually coming out of the Lincoln Tunnel, AWAY from the city
When Nick and Norah are in Electric Lady Studios and Norah receives a text from Caroline that reads "Foumd Flufdy" the date for the text says "Apr 20 2008." April 20, 2008 was a Sunday, and in the beginning of the film while Caroline and Norah are in school, Caroline says to Norah that it is Friday. Since they were out in NYC throughout Friday night into Saturday morning, it should have been April 19, 2008, but it could not have been the 20th.
When Nick is driving to his gig in New York City, he is shown driving the wrong way into New York. If he were coming from Hoboken, he would be driving down the ramp (the helix), into the Lincoln Tunnel. His car though is shown driving up the helix, which would mean he would be coming out of New York, not going in to New York.
The scenes at the Port Authority Bus Terminal show employees wearing "MTA" uniforms (ticket clerk and cleaning woman). The MTA does not operate the PABT and certainly would not be involved with any buses to New Jersey. The scenes definitely appear to be in the PABT, but those responsible for the costumes must have assumed they were supposed to be in Penn Station (where MTA operates the Long Island Railroad). Maybe the book had them being from Long Island.
In the Port Authority scene, there are 3 errors. First the van pulls up on 8th ave in the taxi lane and parks. All the occupants get out and go into the Port Authority building. The van would have been taken almost immediately. Second error, The booth Caroline goes up to is not used for NJ transit which she would have needed to get back to Englewood. It seemed to have been used strictly for its proximity to the bathroom entrance. Third, in the "sandwich" scene Caroline is sitting with the sandwich guy in the main ticketing area on a subway bench. These benches are not located in the Port Authority, (except underneath in the subway) and there are no benches at all in the Port Authority ticketing area due to the lines that form there. It would be in the way.
When the characters are at the Port Authority Bus Terminal, looking for Caroline, they see a large placard showing the bus schedule. It incorrectly shows the destination of bus 167 as being to Weehawkin. The 167 bus actually goes to Teaneck.
When Norah takes Nick inside her dad's studio, he picks up a Stratocaster and says "it's left-handed." Nick is correct; this is a right-handed guitar that is strung upside down with the strap switched for use by a left-handed guitar player. That is how Jimi Hendrix played. The scene takes place in Electric Lady Studios, which was the studio Hendrix built as explained by Nick in the movie and hence, we are to assume that this is one of Jimi's guitars.