Interesting, and quick, read in the New York Times about the effects of music when you exercise. In short, it helps up to the point of intense (that is full-out, 90%+) effort. Up to that point, the music distracts your busy conscious mind from dwelling on how tired you think you are when you’re running, cycling, training for that triathlon. At full effort, your body demands your brain’s attention and the music doesn’t matter too much.
This is about what I’ve experienced. Long runs, music is great. Intervals and sprints, it’s just noise. How about you?