It's the law over here to always were a helmet, but when I have been in other countries (USA, Europe, UK) that do not require it - I still wear my helmet.

Conditioning? maybe, but I have had two accidents (one on the mountain bike, one on the road - clipped a wheel) that destroyed two helmets. I would rather that be the helmet than my head. There are enough risks on the road for me, without me adding to it.