I use a lot of background music while I work. Right now, I'm listening to a 45 minute long techno song a friend of mine sent me a link to some months ago. Usually, I use Pandora -- a channel I started by seeding Plumtree and refining from that point. Sometimes I set up a youtube playlist, or, even more rarely, listen to an actual CD. In the past few days, I've been having trouble finding a satisfying soundtrack -- that perfect mix that helps me slip into a state of flow. Plenty of artists write about this -- it's different for everyone, but you generally need something good enough, engaging enough, that your mind can sort of float on top of it, but not so engaging that you can't focus on your work because you're paying too much attention to the music.
For me, that tends to mean something upbeat, a bit grungy, and if there's lyrics they've got to be not-too-clear. I can't listen to classic rock, because it's almost impossible to not sing along. But I can't really listen to jazz, either, because even if there's no lyrics the music is too pronounced to let it drift into the background. It demands attention.
I'm sure that's not the only ingredient to flow, and it might not even be the one that's been out of place lately. But it's been on my mind.