First up, I'm not interested in a debate on the merits/uselessness of bike helmets. Wear one, don't wear one, whatever makes you happy.
I am interested in their design. I once got into a discussion regarding one of my old lids: I faceplanted at fairly high speed on a road, and the helmet (nearly new MET) had a clean split, right through, at the point of impact. I considered this to be a good thing - it had absorbed the impact by breaking, and while my face was a complete mess for weeks, I only had minor concussion. However, I was also told by a few people that it should never have actually cracked all the way through, and that a decent helmet should always remain completely intact during an impact between the head and a stationary object.
Any informed opinions? Or half-baked ones?
...pretend here is reality, and not some expectant itch of july...