The four cast members that made up the band "Sex Bob-Omb" spent several weeks learning how to play together as a band. Mark Webber, Alison Pill, and Johnny Simmons all had to learn their instruments from scratch, while Michael Cera had to "dumb down" his bass playing in order to not outshine his band mates.
Edgar Wright obtained permission to use the famous theme music from the SNES game, The Legend of Zelda, by writing a letter to Nintendo, saying that it is considered to be "the nursery rhyme of this generation". Several sound effects from the game can also be heard throughout the scenes in Scott's band practice room. Wright was also allowed to use the Seinfeld (1989) theme music for a sitcom-style sequence.
Anna Kendrick, as the character Stacey Pilgrim, wears the actual name badge of the real-life Stacey, on whom the comic creator, Bryan Lee O'Malley, based the character.
At the party where he talks to Ramona for the first time, Scott holds up a very badly drawn picture of Ramona and asks if anyone has seen her. Director Edgar Wright said Scott was originally supposed to hold up a picture of Ramona from the comic book series, but felt the silly drawing Scott holds up was more comedic.
When Scott opens the door to receive his package, Michael Cera actually did throw the package over his shoulder into the bin after 33 takes (most of which are seen on the "outtakes" of the DVD). In a film with so much CGI and SFX, director Edgar Wright wanted the throw to be real for the authenticity. However, the signature shown on-screen was a visual effect superimposed onto the paper.
Michael Bacall: The co-writer of the film can be seen at Julie's party and he's also the guy who asks, "Is he a pirate?" during the Matthew Patel fight.
Bryan Lee O'Malley, Hope Larson: Immediately following The Clash At Demonhead's performance at Lee's Palace, you can see the writer and his wife talking at the bar.