Bicycle Helmets Don't Work
Since the mandatory bicycle helmet law is rearing its ugly head here in Austin again thanks to the efforts of former mayor Bruce Todd, the following analysis of actual real-world results of increased bicycle helmet use in other countries is particularly relevant now.
The New York Times covered this for the USA in 2001. In short: Bicycle helmet usage went way up, but head injuries and fatalities didn't go down. This matches the observations in Australia, the UK, and many other countries.
Ride with a helmet if you want. But don't get smug about those who don't - they're NOT "organ donors", they're NOT stupid, and they're NOT irresponsible. THEY'RE actually the smart ones, given the apparent lack of benefit to wearing bicycle helmets.
And, please, stop the bullshit analogies with regards to seat belts. Nobody ever stopped driving because of seat belts, and even if they did, why would we care? Bicycle helmets are hot, uncomfortable, and inconvenient - and results in country after country show that many people simply stop cycling when their use is mandated. You don't have to carry your seat-belt around with you when you park your car; your car likely has air-conditioning; you're not actually exercising when you drive; seat belts are built in to the car; etc. Oh, and don't forget: seat belts, unlike bike helmets, actually WORK. The analogy couldn't be any worse if they tried.
If it's so damn obvious that people with "something up there to protect" would naturally choose to wear bike helmets, then why is it also not obvious that the same people would do so when driving their car? You get the same impact protection; but you're not sweating and you have an easy place to stow the helmet when you're done (inside the car itself).
Wikipedia has outstanding, heavily footnoted, coverage of bicycle helmets, if you don't like the "cyclehelmets.org" people.