People have touched on a few good points here. First of all walkers NEED to walk on their half of the trail on the right hand side. Cyclist should ride at a prudent speed, slow down, ring a bell or call out "on your left". There is no reason that everyone using a little common sense cant all use the trails.
One last thing. I know it will raise the ire of those doing it, but the head down racer boy wannabes are the worst offenders I see. They ride as if they own the trail. If they want to ride at a higher speed, they should get on the roads and streets.