Composer Harry Gregson-Williams heard a boy (Brian O'Donnell) singing on the street for money in Dublin when he arrived to spend a few days on the set of the film. Later, he tracked the boy down again and recorded him singing six or seven folk songs acapella in a quiet alley. Gregson-Williams chose "Fields of Athenry" from the recording and added his own music around the song.
While watching a football match together, Veronica (Cate Blanchett) tells to the "Tattooed Boy" ('Colin Farrell') that "once she met Eric Cantona" (famous football player from the '90s). Blanchett and Cantona worked together in Elizabeth (1998).
One of the characters in this film was based on actual gangster Martin Cahill (pronounced: Kah-hill). Cahill was the subject of John Boorman's film, The General (1998).
The dance scene where Veronica dances with her family to "Everlasting Love" was added in on the spot by Cate Blanchett.
The Irish Film Censor, who passed the film with a 15PG (now defunct, but equal to 15A) certificate, acknowledged on the official Film Censor website, that had this film been fiction, or of any other plot source than it was, it would probably have received an 18 certificate.
A daily Irish newspaper recently reported that Portlaoise prison (where John Gilligan and Brian Meehan are incarcerated) screens the movie at least once a month in the prison common hall at the request of the prisoners.