Bike Noob, a blog written by a "biking newbie", has an interesting article on helmet safety and effectiveness over here entitled "Helmets - not as safe as they're cracked up to be?"
The article discusses a study by Dr. Keatinge, who is a member of the editorial board of the Bicycle Helmet Research Foundation. Apparently in Dr. Keatinge's review of the available literature on the efficacy of bike helmets, there is "[n]o clear evidence from countries that have enforced the wearing of helmets" showing they do any real good to the wearer in an accident.
In our course of representing numerous bicycle riders who have been injured in a motor vehicle accident while riding their bike, we have found that a good number of these riders have come across the same studies and usually have a done a good deal of research into the question of whether or not wearing a helmet is even worth the trouble. Some of them, unfortunately, have chosen not to wear a helmet, and because the literature is inconclusive, one can hardly blame them. We've even reviewed studies suggesting that the wearing of a bike helmet makes the rider statistically more likely to be involved in an accident with a motor vehicle.
Bike Noob ends the article with sage advice:
I’ve fallen three times in the last nine months. No serious injuries, but all three crashes were my fault. That’s a pretty good indicator that I’m likely to fall again. A helmet won’t save me from my own stupidity, carelessness, or inattention while riding, but it will improve the odds that my noggin won’t be damaged if I do go down.
We agree. Though we don't have a statiscally significant sample of bike wrecks to draw from, in our experience, riders who have worn helmets walk away from crashes that riders who do not wear helmets never get up from. On the flip, we'll look at the standard a little more closely.