I don't wear a helmet to save my life, I wear one to save my ride. In the past 5 years I've gone over the bars about 4 times, some worse than others, and all of those times my helmet had minor contact with the ground, but nothing more than a mild concussion. I would guess that had I not been wearing the helmet, I would've at least gotten a gash that would likely have ended the ride.

BTW: Pedestrians should really be the ones wearing helmets: Why it makes sense to bike without a helmet ? Howie Chong : Howie Chong