The scene in which Hugh Grant's character watches himself in a video clip on the Internet is the video of the actual acceptance speech given by Hugh Grant in 1995 when he won the Golden Globe as the Best Actor in a Comedy/Musical for Quattro matrimoni e un funerale (1994). They dubbed the speech to reflect the fictional movie screenplay at the center of The Rewrite.
Portions of the film were shot in and around Binghamton, NY and the nearby Binghamton University. This is because director Marc Lawrence is a graduate of the university, and has expressed a great love for the school and his experience there. Portions of the film were actually based on his own experience going there.
When Allison Janney's character says her students think she is like Elinor from "Sense and Sensibility" and Keith remarks he's familiar with that character, it's probably an in-joke because in Ragione e sentimento (1995), Hugh Grant played Edward Ferrars, the love interest of Elinor Dashwood.
The carousel seen in the film is the same carousel as the one that can be seen in Now You See Me - I maghi del crimine (2013). The carousel was also used in the movie Face/Off - Due facce di un assassino (1997).
Marisa Tomei was offered the role of Carrie in Four Weddings and a Funeral, but turned it down. She has reportedly expressed regret over this decision. However, she finally got her chance to be Hugh Grant's love interest in this film about twenty years later in 2014.