I don't always keep my camera charged but for the most part it's on a prominent spot on my helmet. People hate being recorded (funny considering the number of security cameras and such all around you) and many of them act a little better knowing they're being watched. When Google Glass improves and everyone assumes cyclist glasses are doubling as instant-youtube-upload minicomputers I might stop wearing them, until then it adds a slight bit of peace of mind. It's silly to expect them to do everything for you, but it sure as heck doesn't hurt to be wearing one.