I must admit, the only reason I don't, is because I find it uncomfortable to wear earphones under my helmet. Not from a distraction point of view...
I saw some moulded earplugs you can get though, that you can also plug into an ipod etc, so maybe they might be worth a shot as they don't 'stick out' from your ears and drop out when you squeeze your helmet on...
or I might try this....
http://www.howtogeek.com/57481/how-t...-ear-monitors/