Most of my writer friends use it in some form. Except for one. She writes while she watches TV. But, in general, my writer friends all utilize music in their writing.
My iPod has my (and my daughter's) entire music collection. So, I often put in on shuffle and listen to the random selections as I work through a literary problem. (Doing it right now... Sixpence None the Richer is on, Salt N Pepa before that.) Some times being out of control of the music leaves me to look at a problem from a new direction.
I also have playlists. These are usually for the car, when I'm brainstorming a scene. I have playlists for romantic scenes (usually dedicated to a specific couple, like good, old-fashioned mix tapes), others for sex scenes, others for fights and others for making up... I have playlists that bring to mind certain characters, and help me get into their POV; and playlists that those characters would listen to.
For example: Adelaide, my 25-year-old former American supermodel-- born in 1978, listens to Placebo, Depeche Mode, Noir Désir, Cake and Salt N Pepa. But her boss, 40-something Étienne d'Amille prefers Jazz, some Norah Jones, Melody Gardot, Django Rheinhart and Juliette Gréco, and anything from the James Bond movies. And Carla Bruni's music amuses him to no end. Now, his wife, Basilie, she likes Jazz but prefers classical. She adores Joshua Bell.
I've purchased CDs because I thought these characters would like them.
Now, the playlists geared at helping me write about these characters are different. When I write about the bad guys, I listen to a playlist my husband made: Chevelle, Prodigy, Nine Inch Nails, Limp Bizkit, Radiohead, Pixies, Tool, The Toadies, Alice in Chains...
And these are all different from the soundtrack for each book, which is usually compiled after the first draft of a novel to keep me focused during revisions. In some cases, they creep into the story, some more clearly disguised then others.
From the opening chapter of the first book of my Fashion and Fiends series:
Competing with the country music from the bar, distant rock music assailed his ears screaming ‘dazzled and doused in gin' about changing tastes in men. A convertible zipped so close by him it lifted his shirttails. Galen broke from his prey. The music blared from a powder blue Mercedes with top down.
It's "Taste in Men" by Placebo from the album Black Market Music.