There was an interesting article along with statistics in "Flight safety" magazine a few years back (Cant find it at the moment). Basically it pointed out that in all rescue service helicopters and military operations use of helmets is compulsory. The various benefits of a helmet is well documented in the article. I don't suggest they be made compulsory. However after reading the article, it is something worth thinking about. It may not save your life. However, even prevention of concussion would be a worthwhile outcome.