I usually wear a helmet, but have been leaving it off sometimes in the heat. My rationale is, if I overheat with a helmet on, I'm more likely to make mistakes! When I was a kid I had a Schwinn 5 speed with the banana seat and used to do crazy stuff on it and wiped out a few times, and it didn't kill me, maybe I was just lucky. None of us wore helmets when I was a kid (I'm talking the '70s, not even sure they made helmets for cyclists then), and there were some fairly steep hills in my neighborhood that we would bomb down, nobody ever got hurt that I remember. That said, I think its a good idea to wear one, even tho I am hypocrite by saying that, since I take mine off if the weather makes me uncomfortable.