I have been asked periodically about my feelings on bike helmets. Here's my stance in a nutshell:
1. I wear one nearly every time I ride. 2. Two to five days a year I do NOT wear a helmet when I ride, usually a short trip in the neighborhood on residential streets. I always ride alone when making this choice so that family, friends and ride organizers don't give me grief. There are people in my life who love me, who are bigger than me, and who would kill me if I did not ride with a helmet. I feel their love, and wear a helmet on 99% of my rides. I suspect that if they find out about the 1% of rides where I go helmetless, I will not hear the end of it. 3. I think mandatory helmet laws for minors under 18 make sense. 4. I think adults must be allowed to decide for themselves whether to wear a helmet or not. 5. The research on helmets is varied and not entirely conclusive. Helmets do not -- and cannot -- protect the head adequately in every crash. (Given the choice between wearing a helmet and ending up a vegetable, and not wearing a helmet and ending up dead quickly, I might be inclined towards the latter.) 6. I believe that while helmets are a good idea, they distract from the real conversation we ought to, but do not, have: that riding a bike in a car-centric landscape is really what informs most helmet use, and that mandating helmets for all bicyclists is an insidious way of letting car drivers and those who legislate/enforce traffic laws off the hook.
Another excellent discussion about helmet use can be found here.