Most likely almost no one will return the greeting. This bothers me, especially when I am running and see someone else who is running, I make a concerted effort to say hello and smile at them. I am almost always met with a funny look, or they just keep looking ahead and pretend I'm not there. Has our society become so self-conscious and uptight that it isn't acceptable to be friendly?
I think this is especially strange behavior between two people that are running, but maybe I'm the only one that thinks there is some kind of bond, a mutual understanding of how miserable running can be at times, and an understanding of how no matter how miserable, we always feel better after a run.
Call me crazy, but I'm going to keep saying hi and smiling at people like an idiot. Join me if you dare.