Ouch, yes I have, a couple of times actually. Most of the time I'm ok, but once I fractured my wrist. OUCH! I was actually barely off the ground (hanging onto a low-hanging branch), but the branch was slippery and I slipped off. It would have been fine (grass underneath), but there happened to be a plastic barrel there which I snapped my wrist against. I had a cast on for a few months :-(