[adambatkin]

The only good argument (in that article anyway) for not wearing a helmet seems to be the Bath university study, which everyone has been citing since the day it was released. But that's the only study I have seen on the topic. The fact that other modes of transportation (walking, driving) would theoretically be safer if you wore a helmet is irrelevant. And it's possible that helmets would turn someone off from cycling, but that seems like a poor reason to not use a bike.

[knowtheory]

There's a PLOS One paper which reanalyzed Ian Walker's 2007 data and claims that the effect Walker demonstrates is illusory if you chose different classification criteria for how to group data points: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjourna...

I tweeted w/ Ian Walker a bit about it, and though he hasn't written up a reply he disputes their conclusions (just for full disclosure).