Norah is a Jewish girl attending a Catholic high school. This is explained in the book that Norah wants to attend any school Caroline does, but due to Caroline's obnoxious behavior, she's kicked out of every school she's been to and is only accepted at a Catholic school.
Ari Graynor (Caroline) improvised her whole speech at the Port Authority when Kevin Corrigan decided he wouldn't say a word during his scene.
The film originally opened at The Jerkoffs show where Norah first meets Nick. All prior scenes (including Nick leaving a voicemail on Tris' phone, the scenes with Norah, Caroline, and Tris at the Catholic school, etc.) were re-shoots filmed six months after principal production was wrapped.
Cameo: [Rachel Cohn and David Levithan] The authors of the novel are in the background of the Veselka diner scene, sitting at a table.
The trailer shows an alternate version of the club scene kiss with Nick and Norah. When Tris comes up to ask them how they met - it is Nick who tells Tris that they have the same dentist. In the actual movie, Norah is the one that tells this to Tris.
Nick's cellphone ring tone is "Boy's Don't Cry" by The Cure.
The title character's names are a reference to Nick & Nora Charles, the characters in the 'Thin Man' series of films based on William Dashiel Hammett's book.