I tend to like music in podfic if I like the music itself and find it appropriate to the story (and the volume is all right, etc). I've never used it myself, but I think that has to do with me being lazy. Sure, it's not hard to do, but I've never gotten around to doing it and have seldom felt inspired to do it, although I do love music and consider myself a musical person. Maybe I should try it just as a challenge to myself.