Check out Jake's discussion of what constitutes Christian music. I think it is a hard question to answer, at least if you want to be consistent with other areas of your life. The problem, I suppose has to do with how we categorize art. Does it matter what the faith commitment is of the person who wrote the lyrics? Or the singer? Or the other instrumentalists? Well, to some extent it is going to have an influence on the song. On the other hand, if a Christian sings a song about a kitchen chair, is that a 'Christian' song?
I am not ready to throw out the term Christian music just because it is slippery. There are certainly some songs which are explicitly Christian, as well as others which explicitly are not. As for the gray area in between, I will be interested to see what Jake concludes when this is all done. In the meantime, it is worth checking out Patrick's theology of Indie Rock from last January. I don't agree with everything he has to say, but you will be repaid for the the time it takes to read and think it through.