I often encounter hikers on the local singletrack trails near where I live, so I'm a bit careful about downhill speed where visibility isn't good. Many of them will step off the trail, but I never expect them to do that as a matter of course. Hikers don't bother me (I'm often a hiker myself), but horses are another matter. Most horses that you meet on the trail have been pretty well trained, but a couple I've encountered have freaked out (even after I've stopped) and nearly thrown their riders. I always stop and ask if it's OK to proceed when meeting a rider on horseback.