Depends how you fall, how fast you're going, how high you're jumping etc.
It's definately a real danger but you can also break bones from your bike or just running and falling.
Falling down some steps would be disasterous.
I'd imagine a nasty tumble at high speed would result in fairly serious injury.
But it's all fun right? Just make sure you have wrist guards on and a helmet (even if u only wear the helmet when trying new things. It can save ur life).
