I find that if I play Matrix disco music I can pull a 900, if I listen to Bob Dylan I can barely land a 180.
I used to listen to music all the time.. it changes the tone of your riding (both abilities and ambiance). The biggest issue I ran into is people would try talking to me while riding and not see the ear buds under my helmet, or I would ride by a guy and smile and wave not hearing his screams for help.
I then switched to the giant DJ style Skull Candy headphones that fit over my low profile moto style helmet. This way everyone around would know I 'was not listening' to them. After breaking 4 pair of those in 2 years I went back to less expensive earbuds. The trick is having an accessible for volume and pause controls, otherwise you are peeling off gloves and zippers every time someone asks you a question.
The new helmets like Tom mentioned or the integrated jackets with ipod control might be interesting. I am planning on installing my broken Skull Candies into my old paragliding helmet for a nice surround sound while riding. I was also thinking of going 80's skier style with a boom box in my backpack for the broes to enjoy when I pass them on the race course.
BTW - I find Drum & Bass Techno and Heavy Metal to be the best to ride to.