The Cast Showoff: Real-life blues singer Chris Thomas King plays Tommy, and at one point gets to sing (in his own voice) a rendition of Skip James' "Hard Time Killing Floor Blues." Also, that's really Tim Blake Nelson singing the lead vocal on "In The Jailhouse Now".
Half-Remembered Homage: Though they based the story off The Odyssey, The Coen Brothers admitted to having never read it, instead basing the script on adaptations they read or saw as kids, particularly the 1954 movie version starring Kirk Douglas.
Non-Singing Voice: Dan Tyminski, a member of Alison Krauss & Union Station, provided Everett's singing voice as George Clooney proved not to be up to the task. Reportedly extremely humiliating for Clooney, as he's from a line of well-known singers.