I have it on 100% of the time unless I decide I need to hear the engine for some reason.
I have a ridin' hard playlist of all the rock stuff. That's what I listen too around town. But in the twisties? I listen to Glen Gould playing Bach's "Well-tempered Clavier." For some reason, hearing all that piano gets me riding a LOT more smoothly and carefully and I actually produce a faster overall ride, just because of the relaxation factor.
Music, of course is up to the rider. If you're an ADD mogul, it shouldn't be a problem at all! But if you find that it's distracting and takes away from your ability to ride safely, turn it off.
--Wag--