Director Cameo: (Karan Johar) (plays a man talking on a cell phone behind Shahrukh Khan inside the train during film's climax.)
Ajay Devgan was the original choice for the role of Rishi, but he refused.
Kajol was initially offered the lead role in this movie, but due to scheduling conflicts, since she was already cast in Fanaa (2006), she had to refuse. She was originally going to play the role played by Rani Mukherjee, and Rani was to play the role played by Preity Zinta.
The idea of making this film struck Karan Johar while he was in London. During his trip, he saw the movie Before Sunset (2004), based on a couple who meet after parting ways. After seeing that film, he was out at a restaurant where he overheard a married couple breaking up amicably. The incident moved him and he decided to explore the idea.
India's most expensive Hindi film, reportedly made for an astronomical Rs 70 crore (~US$15 million).
Amitabh's role as sexy sam is considered to be his worst ever role.
One critic had pointed that if he saw Rani cry in any film again he will jump from the balcony.
Karan Johar asked Shah Rukh Khan, because he was busy elsewhere, to direct the controversial hotel scene himself. Khan then asked Amitabh Bachchan to direct the scene by phone because he was uncomfortable to do it.
The role of Srk's son was played by a girl.
The makers of the film came up with T-shirts for the film's promotion. The T-shirts had the witty phrase "married or happy" on them.
The film was primarily shot in New York, where there was a 90-day schedule. The remaining scenes were completed in four of Mumbai's studios.
During the garden scene where Shahrukh convinces Rani for marriage he states his own House name "MANNAT".
Director (Cameo ) Ayan Mukherjee appears in the song Tumhi Dekho naa carrying gift boxes
Saif Ali Khan and Ajay Devgn were the original choices for the role of Rishi, but both declined due to them both working on Omkara (2006).
Karan Johar: plays a man talking on a cell phone behind Shah Rukh Khan inside the train during film's climax.