Here is another story about helmets doing their job. Time for me to pass the torch of wisdom.
Something weird happened en route tonight. I'm not sure exactly what, but I was going about 19 mph and had to hit the brakes. The front brake siezed up and I went flying over the handle bars.
My helmeted head crashed full force into the edge of the curb. There is no doubt that it would have smashed my mellon and either killed me or wiped out half my memory.
Now the skin on my fingers are peeled like a banana and my neck is getting stiff as the night progresses, but I'm alive and on the bikeforums rather than being in the hospital or worse.
When I first started cycling for real (for function instead of just for recreation), my full-time bicyclist friend made me promise him that I would always wear a helmet. He was wearing one when he was hit by a car and it saved his life. I made the promise and kept to it for years. Remember that when I made the promise, helmets were a lot dorkier than they are now and they were seriously uncool.
Now, I pass the torch of wisdom to you. Wear a helmet always. It's not just for when you get hit by a car. Other stuff happens too. Make sure your friends and family wear one too.