Kareena Kapoor was writer/director Imtiaz Ali's first choice for the role of Geet. Even though he wasn't particularly a fan of hers and hadn't seen her in many movies, he knew she would be able to look natural without makeup, be hyper, talkative and interesting but not irritating.
The producers had first signed Bobby Deol in 2005. The film had many working titles at the point. "Geet" was one of them. Bobby told the producers to sign Imtiaz Ali because he was very talented .The producers wanted Kareena Kapoor for the film , but Kareena refused to even meet Imtiaz Ali. That is when Bobby suggested they approach Preity Zinta. She agreed but needed six months before she could shoot. This is when Kareena told the producers she would sign the film only if they replaced Bobby Deol with her then boyfriend Shahid Kapoor . The producers agreed and replaced Bobby Deol without even informing him.
Writer/director Imtiaz Ali only settled on Shahid Kapoor for the role of Aditya after meeting him, as he previously viewed him as a "forgettable actor" before realizing that he had "gone through a lot in life and that maturity had never been brought out" and that as such he was perfect for the part of a "young, mature, quiet guy."
Kareena Kapoor and Shahid Kapoor who play lovers in the film were also dating in real life - until they broke up whilst making the movie.
Dehli's PVR Cinemas held special screenings of the film on Valentine's Day 2008 to celebrate its 100 days run at the box office.