In a movie about people who would stop aging at 25 years old, many of the actors, including Cillian Murphy and Justin Timberlake, were in their late 20s and early 30s. Amanda Seyfried, however, really was 25 years old during filming.
Sci-fi writer Harlan Ellison launched a lawsuit against New Regency and director Andrew Niccol, claiming that the film's plot bore an uncanny similarity to his short story "Repent Harlequin! Said the Ticktockman". Initially, Ellison was seeking an injunction against the film's release, which he then watered down to a request for onscreen credit. Ultimately the case was dropped with no money exchanging hands between any of the parties.
The trivia items below may give away important plot points.
The building used for the big bank they're going into at the end, is often used for courthouses in many movies and television shows. The building only has 4 stories, but additional stories were added by CGI.