I've had around twelve one hour sessions, where I've been in groups of eight to having it all to myself, the best groups seem to be where there is more than one person riding, as its pretty tiring after an hour.
My first session was cut short due to arriving late and having to watch a safety video and I managed two runs on the standup board and managed to give myself whiplash for about a week, when I fell backwards.
This video was about my second or third session where I do stay upright for a short time, and yes, that did indeed hurt.
We then forward to this morning, when I've managed to improve, with my balance being almost spot on, though I did manage to land on the top edge, which was uncomfortable.
The thing is I'm now finding is brusies in odd places, like just above my toes and my knees. If you get the chance to use the flowrider, give it a go, its such good fun and should you like to see all my videos, visit http://www.youtube.com/user/wildheartbaby?feature=watch