I've used this one for some time, and it does indeed work:
When I walk through large crowds of people, to avoid walking into anyone, I simply stare at my destination. I look no one in the eyes. People actually will watch your eyes and they avoid the direction you are going. If I look into people's eyes as we are walking into each other, we are sure to collide. You have to let people know where you intend to go with your eyes. It always works for me, try it!
How many times do you make eye contact, then you and the other approaching person juke back and forth and nearly collide anyway? Just act distracted and don't make eye contact. Problem solved.
The link to Ultrarunning is that this really doesn't apply much. First, not all races have sections in which you face opposing runners. In training runs, the number of people encounters is pretty small anyway. I just usually make it a habit--as is the normal rule on multi-use trails--to keep right except to pass.
Never had so much as a close call to hitting another runner on a trail.