Inline skaters should wear a helmet. But what about bicyclists? I wear a bike helmet, and so do my children. It seems to make sense anyone riding on a bicycle path, but today I read that it may not work for anyone riding with cars.
The problem, alas, is the car driver.
Cars are not much of a factor in head injuries occurring during inline skating; inline skaters rarely mingle with cars. Bicycles, however, do. Most bike fatalities and injuries are automobile related.
It turns out that automobile drivers, on average, give more space to bicyclists not wearing a helmet. If you wear a helmet, there's a 23% increase in automobiles passing within the 1 meter danger zone 
I suspect that this is doubly true for motorcyclists, though the researchers did not study that topic. So much for all my disparaging remarks about bare headed motorcyclists; if my guess is right than the decreased risk of automotive impact will far outweigh the decrease in head protection. Aging boomers -- let your residual hair flow free ...
So what do we do while researchers sort this out? If you're not riding in traffic the evidence strongly favors riding a bicycle helmet. If you ride in traffic, however, things are trickier than I'd once believed. There's a case for putting the helmet on the bike rack when entering traffic, and donning it for the bike trail...
I won't change what I do. For one thing surprising results require confirmation, for another I need to reinforce the children's behavior. For them the helmet is an unadulterated good.
In the meantime, let's find out what other things we can do to get more space from cars. How about a horizontal flag that extends one foot left? Professor Walker, please retest with the flag. Let's see what we can do to get those drivers outside the 3 foot limit. Maybe a flag and a helmet together will provide both head protection and a lower impact risk.
 Scientfic American Fact or Fiction, October 2007. Walker et al, Accident Analysis and Prevention, March 2007. The summary didn't mention gender variation. My experience is that women drivers give much less room than men drivers, perhaps because of a greater reluctance to cross the solid center line.