My thinking on this is on the same lines as Pax and JennK. I do wear a helmet about 95% of the time, always in traffic or on rooty/bumpy trails, always when riding with small girl in the trailer, and always when my husband is away for work and I am the solo parent.

I have a background in risk, and feel fairly sure that crossing some of the local roads as a pedestrian is more dangerous than cycling unhelmetted half a mile along a flat traffic-free bridleway with an even surface and clear visibility in both directions, for example. I'll also do a quick spin around the block helmet-free when checking something on the bike - it's a residential area with a 20mph limit and speed-calming measures. It's also very common for children to be playing in the road in this area so traffic is careful. Even my route to nursery is chosen to be as quiet as possible, I generally see no more than 5 or 6 moving vehicles on the road sections.

I did blog about helmets recently. A roadside assistance business here recently polled its (motorist) members and found that a huge majority of them wanted cyclists to wear helmets. The result was this organisation has started a programme of handing out thousands of helmets branded with their logo to cyclists over the country. I remain pretty unhappy about this for a number of reasons. That said, I think it is absolutely down to the individual to decide what level of risk they are happy with and act accordingly. Be informed and know exactly what the capabilities of your helmet are.