When you have a helmet on properly, you should be able to shake your head pretty fast and not have it move at all. I've seen a lot of riders with their helmets too far back, leaving their forehead vulnerable.

Unless you carry a mirror around with you, you can't see what you look like with the helmet on. And who is so vain as to care more about their appearance than their safety. Concussions can look pretty unattractive, too.