I have been playing around with my new Go Pro Helmet Cam and I tried mounting it on the handlebars of the mtb.  I must say, this is a no go.  Its pretty amazing how much the handle bars twitch from side to side during a normal ride.  I am the one that did the filming and even I got sick watching the video.  This morning I moved the mount up to my helmet so hopefully that will turn out some higher quality videos.  I think, in general, it is a much wiser move.  On the handlebars, you would see the bike come up to a pretty cool obstacle in the trail, then would see the sky, then the ground as I went up and over it.  I think with it on the helmet, you will be able to see exactly what I am seeing and hopefully have a better view of what it looks like to do a little mtbing.  At least, that is my thought and plan.