Riding the Gateway trail I usually come across horses and their riders. The trail is really two trails in the section I ride: a paved multi-use trail and an unpaved horse trail. The rules of the trail say that those on horseback using the horse trail must first purchase a permit. Other users are also allowed, and are not required to buy the permit.
Most riders are very congenial, and all the horses I've approached or passed are very calm. However, I've recently decided to dismount or where possible to ditch over to the paved trail when passing or approaching two or more horses. Even though they've always been calm, they are big beasts and haven't had much experience with unicycles before so I don't want to cause them to bolt, particularly with a student rider.
Here's a brief encounter with a pair earlier today. I was pretty tired and coming to the end of a 10+ mile ride, but really it wasn't any trouble to dismount, walk by and greet the riders. They seemed a little snarky for some reason, but that's their problem, not mine.
Also, for the first time ever, I came across two other unicyclists. We passed by each other on one of the bridges and I think all of us were surprised. They had some tricked out 36" touring unicycles with bars but I didn't catch the type, and of course I forgot to turn on the video camera!