Well, now we have a study:
I have to say, I feel vindicated. Statistically, the helmet won't make me less likely to die, yet it will make me look like a dork. I gotta continue to go with the bare head (except when Darcy is looking).
[Legislating a] new helmet law reduces bicycle deaths among [children] by about 19%. It doesn't affect older riders. Since serious bicycle accidents are rare, however, the absolute numbers are still small, about eight fewer deaths a year among kids 5 to 15 than would otherwise occur in the states with helmet laws. "It's not a ton of lives when you compare it to something like wearing your seat belt," says Prof. Stehr.
One reason for the drop is, of course, that more kids [are wearing] helmets when they get into accidents. But another is that many give up cycling altogether. Using surveys of parents, the professors find that about 650,000 fewer children ride bikes each year after helmet laws go into effect. That's about 81,000 fewer riders for every life saved. Helmets may save lives, but the dork factor also takes its toll."
Note 1: This battle is being waged full tilt over in the Netherlands, where helmet advocates are pulling out all the stops to get kids to strap them on. It doesn't seem to be working as helmeted cyclists are getting odd looks and are getting accused of being friggin' Germans.
Note 2: As we all know, for every problem there is a technological solution: The invisible bicycle airbag. With a video.