There certainly have been light aircraft accidents where the use of or lack of a bonedome has made the difference. I recall a case where somebody was despatched by an altmeter setting knob to the forehead, something that would have been survivable with a helmet.
The use of safety equipment is frequently debated in here and in private flying comes down to an individual's risk tolerance. Whilst many think that the use of safety equipment looks uncool or pretentious, wearing unsafe clothing looks reckless and stupid to those who are familiar with some of the potential hazards. Safety gear may be needed rarely or never, but it only has to save you once for it to have been a smart move.
I've seen an interesting trend amongst 16 year old moped riding chavs who are presumably of the 'safety gear is uncool' doctrine. In order to comply with the letter of the law and avoid the attention of the constabulary whilst guaranteeing the absolute removal of any safety benefit, many kids ride around with the helmet perched on the back of the head with the chinguard up on their foreheads. Darwinism at work.
