Started wearing a helmet to ski this year. I felt a bit of a prat at first to be honest, but having had a few head knocks in the past and seen others suffering worse, decided that I'd just get on with it. I've not bumped my head since, but I do feel safer now with it on. I expected a load of funny looks, but apart from those I probably get behind my back I've not suffered any humiliation yet!
In the aircraft, I'm considering getting one for use on water crossings with my children on board. For me... not the children!
The thought is that I sort of owe it to them to make sure if we do ditch that their only hope of getting out hasn't gone and knocked himself out! If one of them is knocked out, I can help them. If it's me we are all doomed!!
Having said that I'd probably keep the thing hidden in the aircraft and stick it on once airborne!!