Another (related, I promise!) question; can a show have more than one "I want" song?
When I got to see book of Mormon I deliberately had never listened to the cast album, and other than "Hello" (on the Tony Awards broadcast) I came in a complete virgin to the jokes, the music, and the lyrics.
I seem to remember thinking a couple of times early in Act I, oh, here's the "I want" number (getting your mission, wanting your mission to be in a specific place, etc.) but when the show gets to Nabulungi singing Sal Tlay Ka Siti I though, here it is, the real "I want" song and the heart of the show. This is the point where I locked into what the show was about -- wanting something better, ever if you don't have all the information in front of you about what "better" constitutes. For me, it enlightened the actions of every other character and it was an amazing moment.