I got my OneWheel about 2 weeks ago. I had about 2 days to ride it before vacation, rode it <some> while at the beach, and have been riding it non-stop since we got back this weekend.
I'm very happy with it, haven't had it off road much (nothing but rain since I got it).... so most of my riding has been gravel roads with nice hills. Per recommendations here I started off with it in extreme mode, somewhat surprisingly I got on it the first time, road around the yard, turned, went over some nice humps, never fell off or lost balance. It feels really natural coming from a skating (ramp) background. That said, later in the day I was carving off a dirt hump / lip and went down hard into gravel.
I've already found some interesting tricks... probably already known, but I wanted something between extreme and elevated mode. So when I turn it on, I put it on level ground with a 3/4" block under the wheel. With it in extreme mode this puts the ride position somewhere between extreme and elevated. I'm not sure what logic they use, if it re-calibrates occasionally, etc... but this seems to work well.
I'll post more later, but wanted to share a little and thank you guys again for the tips. People who skate / surf / snowboard really should try one of these. Hopefully the prices will come down and give more people an opportunity to get one.