I'm reading Rex Pickett's Sideways, and there are several references to music throughout the book so far.

Jack plays "the new" Flaming Lips CD on their drive to Santa Ynez.
A girl karaoke's "Landslide" by Fleetwood Mac
A guy karaoke's "Jumpin' Jack Flash" by The Rolling Stones
Miles karaoke's "Crystal Blue Persuasion" by Tommy James and The Shondells
During a panic attack, Miles thinks of "All You Really Need Is Love" by The Beatles

I've got about half the book to go, so I'm sure there will be more. Anyway, I got to thinking about compiling a sort of soundtrack mix to the novel. Has anyone else ever done this? If so, what was the book and how did it turn out?

Sort of...however, it's usually a "Songs from and Inspired By the Novel" kind of thing. My friend and I usually pick a book and create a soundtrack for it. We did that for the Watchmen graphic novel (years before the movie and with better results, I might add). We also did the "trilogy" of Michael Marshall's books, The Straw Men, The Upright Man, and The Lonely Dead. The challenge is each of us make each other a soundtrack, and then compare "albums." We merged our Watchmen soundtracks into an "Ultimate" 2-Disc set, by making disc 1 a collection of songs found in the book itself (mentioned, played or quoted), and disc 2 being songs "inspired" by the book. I must admit, I felt a little bit of pride when "99 Luftballoons" (something I'd used on my "inspired" section) ended up being in the movie itself!

Now, this I think, is a very creative addition to the standard method of book-reading. Imagine the conversations that an entire book club could have, even if each person just selected one song! I realize that few people will even consider this subject, and most of those who are made aware of it will dismiss it, but I tip my proverbial hat to you and your friend. (And kudos on pegging "99 Luftballoons!")