Tell HN: Wear a Helmet
There's some interesting research out there suggesting that head/neck injuries are actually more common among helmeted bicyclists than the non-helmeted.  The factors include the extra weight of the helmet, the size of the helmet causing the helmeted head to strike the ground when an unhelmeted head would not have, and additional risks taken by helmeted riders (think: risk homeostasis).  Unfortunately I can't find the link that was making the rounds a few months ago.In my own personal anecdotes, I have had one major bicycle wreck where I somersaulted into a car, one bicycle wreck where my chain snapped and I flung myself over the bars onto the street, and a couple of low-speed (~10mph) motorcycle offs where I collided with the ground but my head did not touch.  Though there was one motorcycle case where the side of my helmet dragged on the ground slightly from about 5mph; it's arguable whether my head would have hit.That said, I have hit my head incredibly hard snowboarding, after catching an edge at very low speed ("last run of the day!" type thing), and always always always wear a helmet every single time I ride a bicycle or motorcycle or snowboard, just as I always wear a seatbelt in the car. It's just a habit, and a good one.