I was reading an article the other day that a rider competing in cross country had an accident where her horse actually fell on top of her. Normally when a horse falls ontop of the rider, the crush injuries are serious and can be fatal. This rider happened to be riding with a treeless saddle, which actaully absorbed the impact and cushioned the blow of the horse on top of the rider!
If the rider had been using a normal saddle with a tree, she would have received far more serious injuries, because it was a treeless saddle she walked away a bit bruised and winded but relatively ok.
Now I'm not saying that treeless saddles are definately safer than traditional saddles, but its worth looking into isn't it?