I work with someone that has one. Pretty cool toy, but after watching what it takes to pack it along, un-pack it to use it, pack it back up, etc, I really don't see it being all that worth it for scouting rapids.
At least with his setup, I wouldn't be as concerned with losing it or it being damaged, as it can be programmed to fly at a certain elevation on it's own and land in a specific location (down river at your next campsite! LOL), but I just see it as being more of a hassle than it would be worth. It's not quite like a go pro that you just leave mounted and turn on and off as you go...