Haha, Pete blowing through the stop sign in the video bothers me a lot more then the presence/absence of a helmet. Because I live in his general area, and bikers who think the rules don't apply to them irritate all the car drivers, who then are more hostile to the next biker. It's a horrible spiral.
I wear a helmet 90+ % of the time, but not when my very long hair is wet and drying. At those infrequent moments, I figure it's better to do whatever errand it is on a bike then to hyper-optimize. I've also observed that there are enough bikers around here that drivers behave fairly reasonably around them. (Unless they're college students who just came into town, or otherwise not familiar with being here. Alas.) Stv, I always, always wear a helmet when I'm "going for a ride" that will involve a speedy descent. Anything between my head and the road can't but be helpful at 50 kph!