When Mila Kunis changes in the back seat of a taxi, the filmmakers felt the driver didn't sound like an authentic New York taxi driver. So they used Mila's father Marko Kunis to dub his voice. Marko worked as a taxi driver when he first arrived in the United States and still has a Ukrainian accent.
Justin Timberlake's character has a lightning-bolt tattoo, and Mila Kunis' character wears a lightning-bolt necklace throughout the movie except in the photo-shoot scene when they are angry with each other.
The scene that Mila and Justin's characters decide to break it off was originally scripted as them being naked whilst deciding to break up. The idea was then scrapped because the director, Will Gluck, said "It was just wrong."
In the scene were Mila Kunis' character, Jamie, is speaking to Patricia Clarkson's character, Lorna (Jamie's mother), about the benefits of free love and how people behaved in the 1970s, you can clearly see the movie Bob & Carol & Ted & Alice (1969) playing in the background. This is Paul Mazursky's cinematic homage to free love and ties in nicely to Lorna's character "free love" spirit.
The song that Dylan makes fun of and refers to as an "amiguously upbeat pop song that has nothing to do with the plot" at the end of the movie that him and Jamie watch together is called "Hey Soul Sister". Ironicaly, the song is played at the end of the film.