I heard "on your left" on ski area cross trails a couple of decades, at least, before I heard cyclists using it. In Colorado a lot more people are skiers than most places so that could explain it too. Walkers and joggers on the bike trail near me must walk the trail a lot because they mostly respond correctly to either the verbal warning or a bell. There are exceptions of course and ipod owners are in their own ipodland, there's nothing to be done about them. By me there are a whole lot of cyclists that give no warning at all. Then at the other end of the spectrum a fair number of bikers and pedestrians will give you a little wave without looking back to let you know they heard you. If instead of sinking to the lowest common denominator we would all emulate the best practices of our fellow man and woman the world would be a much nicer place.

Ken