I don't ride in a group anymore because the horse I ride is very competitive. Even when we're by ourselves I still have a time controlling him, but in a group, forget it. It makes the people I ride with uncomfortable, as well, because he has a reputation, so I just figured there was no point in messing up their rides as well as rubbing my nerves raw.
What makes me nervous is when the rider in front of you is nervous and keeps looking back at your horse and saying, "please keep him back, please keep him back" and I'm over a foot behind. But anyway :) For the most part I've had very good trail experiences.
"In riding a horse, we borrow freedom." Helen Thompson