I turned the music off in Minecraft. Not because it's bad, it just doesn't really appeal to me. I also prefer to play my own music in that anyway.
I turned the music off in Need For Speed Undergound 2 though, because it was a bunch of rap, pop, and hip hop, none of which appeals to me.
The music in New Vegas and Fallout 3 were both really repetitive so I turned it off in those too.
Usually, I'll leave the music on though because I think that it adds to the experience that the developer was trying to create.