It has been proved that you can kill yourself from falling over on a pavement while walking, unlikely this may be, but it is possible. So imagine how much more likely it is to die if you add more speed and a fall from hight.
Again I don't want to appear to be lecturing people but you would be a fool not to wear a helmet on a bike. If you ride regularly witthout a helmet it could only be a matter of time before you seriously injour yourself.
Four days ago, at the weekend, a friend of mine (who usually wears a helmet) wen't out for a ride, nothing serious just messing arround, at my local skate park. He nailed his head pretty bad there, knocked himself out for 5mins. He's recovering now, but still can't walk. But theres a lesson to be learned there, allways wear a helmet even if your just messing arround, my friend learnt the hard way, and its definately not the best way to learn.
Sorry to go on about it but I think its important
Chris
^^^read above post, some good stats there^^^