Much is made these days of having a multimedia experience, and I believe that Nick and Norah's Infinite Playlist works on that level. The film, due to the nature of the medium, is presented as a rollicking night in New York City. The book is more about being inside the heads of the two main characters. Instead of being disappointed that the film didn't mirror the book exactly, I found that I enjoyed the way the filmmakers rearranged the events. Having read the book first, I had the characters' backgrounds and motivations in my head. It made for a richer viewing experience.
In my review of the book, I said that I wouldn't hand it to my 16-year-old because of all the sexual content. There is sex in the movie, as well, but it seems to be milder. I would much rather have M watch the movie.