I had a friend in college that would put on music whenever she was doing anything that required brain power or else she couldn't think. Her reason was that there was always a song in her head...always. We used to test her on it and she never failed. I think that would be hard to live with...

I use classical or instrumental music when I've got long, difficult computations to do at work because it drowns out other distracting noise without distracting me. Same thing for working difficult homework problems when I was in school. I also use music for running on the treadmill or biking on the trainer because I like to drown out the equipment noise.

Other than that, I prefer silence or the sounds of the world...particularly when I am outside. And I cannot stand leaving the TV on for 'background noise'. It drives me insane!

I also don't do audio books except for long drives (they saved my sanity driving across the country with only my cat for conversation!). I read at more than double the speed of an audio book, so I would never choose one when I wasn't intentionally trying to kill time, either.