Hmmm, most of the xc mountain bike trails here are mixed use. I run into hikers, and horseback riders all the time. In addition to mountain bikers. We seem to all get along just fine actually. I know I sure as shit don't want to hit a horse, much less a person.
Funny actually, last outing at Buff Creek. We had gotten on the Colorado trail and there were a couple of horseback riders with dogs. They saw us and took off galloping down the trail. So we railed it and even though it was downhill, we were not closing the gap very fast. They pulled up at an open area to let us by. It was pretty fun to watch those horses rip through the woods.