I recently found this article that talks about a rangers experience with mountainboarding.  Bottom line is they say that riders do not have much control while on their mountainboard, is this really true?  I believe that with experience comes control, and that the ranger just like many first timers got intimidated by how difficult mountainboarding can be if you do not start slow.

And of course mountainboarding is dangerous if you are new to it and decide to bomb down a steep hill...

Article: 

Where's there's a hill there's a way to enjoy the thrill of mountainboarding