U2 is this week's guest on a podcast called Song Exploder that takes a song and breaks it down with the artist(s) who wrote it, getting them to talk through what inspired them and how it was all put together.
The Edge talks about how he uses Garageband as a sketchpad along with loops put together by U2 drummer Larry Mullen Jr. to mess around with ideas - and eventually putting them together with a different set of lyrics by Bono than what they had originally recorded.
From what I've read and seen over the years, it's a fairly common process for how a U2 song is put together - pieces are moved from one idea to another, lyrics are rewritten, solos redone. I don't think U2 gets enough credit for the care and attention to detail that they put into songs and the subsequent tour. As I discussed with Matt McGee on Daily(ish) #105, they don't just put together a greatest hits song list for their tour - each song is put in it's place with lots of thought.
Listen to U2 on Song Exploder