Pace is extremely important, as pointed out by Rios! It's extremely difficult to enjoy a trail ride with other people, when there's a leader who can't control pace very well.
That said, it's also annoying when other riders behind you can't control their horse's pace, and you wind up in situations where you are having your horse be 'run up' by another horse; good way to ruin a horse who doesn't mind having other horses behind him, or get his heels clipped good.
I think those are the two that are really important on my trail horse list; that and teaching a horse to maintain his gait, even if he IS going toward home...Lol!
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."