It is impossible to follow any cycling website or blog without the Great Debate on Helmets popping up sooner or later. Usually several times and it is best to wear an asbestos suit whenever it happens. :)
Having said that, the latest incarnation on EcoVelo
is quite civilised, well worth reading, and has referenced a fascinating post on the How We Drive
The article is highly recommended but this quote puts both the debate, and the arguments on both
sides, into perspective (and is a timely reminder on how the scientific method works):"The reason nobody knows for certain is that only one method exists for us to get a definitive answer: the experiment. If we took a large number of bicyclists and randomly made one-third ride with helmets, one-third ride with fake helmets (the placebo) and one-third ride with no helmets (the control), then after a couple of years we could count the dead and get the answer we are hoping for. Sadly, however, there are some fairly obvious ethical difficulties with this plan!"