During his audition, Thomas Haden Church stripped naked because that was what the scene called for. He later learned that he was the only actor to do that.
The food that Miles, Jack, and Miles' mother consume during the dinner at Miles' mother's house gave the three actors food poisoning.
During an emotional scene in the film, Miles talks with great passion about Pinot Noir. After the release of this movie, sales of Pinot Noir wines rose by more than 20 percent over the 2004-05 Christmas/New Year period, compared to the same period the previous year. A similar phenomenon was experienced in British wine outlets. Miles is deeply disparaging, in a different scene, about Merlot, and sales dropped after the film came out. Ironically, Miles's prized bottle of wine, a 1961 Château Cheval Blanc, is a blend of Merlot and Cabernet Franc, another grape Miles disparaged.
An entire street was blocked off by the police for the filming of the scene in which M.C. Gainey runs naked down the street. Moreover, the people who lived in houses on said street were paid by the crew to stay inside their homes during the shooting of this particular scene.
Paul Giamatti admitted to faking every bit of wine knowledge, and not understanding why anybody would care about it. He also claims he was shocked that he was cast in a lead role and initially thought it was a practical joke.
Rex Pickett: (the source novel author) The golfer who actually hit the ball when Miles hits the ball back at the golfers behind them. He claims that Paul Giamatti's exceptionally poor golf form made it impossible for him to accomplish the shot.