I use a helmet 99% of the time.
My mate recently had a car pull out of a side road in front of him. He was in ICU for a number of days, and then HDU for another few weeks. He now has a lot of titanium holding his face together, is missing several teeth, has a fractured vertebrae in his neck (fortunately didn't affect his spinal column), and a very nice scar on his temple coutesy of his helmet breaking due to the impact, plus some other supeficial wounds.
If he hadn't been wearing his helmet he may well have bypassed ICU / HDU and gone straight to the morgue, or alteratively been in a vegetative state for the rest of his life!