I'm a firm believer in Murphy's Law. I know that the one brain-crushing accident I'm in will be the time I forget to wear a helmet. And furthermore, whenever I get on a bike without one, I start to panic anyways, so it's kind of a self-preservation thing: wear my helmet, don't panic, don't crash.

As far as fit, I've never had a helmet that cost more than $30. My previous one (a Specialized) was awful. I just got a Giro Transfer, and it is the bomb.