I used to travel for work, and I have a set of Shure in-canal headphones that I bought to use on the plane, these to be exact - http://www.shure.com/PersonalAudio/Products/Earphones/SEModels/us_pa_SE210_content

I've been using these while I ride, and I really like it. I keep the volume low enough that I can hear things going on around me, and since they're in-canal, they block the wind noise from my helmet pretty well. Some folks are telling me I'm nuts, because I should be focusing and listening to what's going on around me, but I really don't think I'm any less focused personally. If I'm not using the headphones, my mind tends to wander anyway, and I end up singing a song in my head anyway.

Opinions? Am I nuts?

"Anyone who has never made a mistake has never tried anything new." - Albert Einstein