I imagine somewhere on a runner's forum is a paralell topic about cyclists who don't share the road with runners-with equally passionate arguments on both sides. I have on a few occasions bike in New York City's Central Park. The inner roadway is closed to cars on weekends, which means that the bikes have the entire roadway, yet, somehow a bunch of bikes always seem to wind up on the designated runner's path, sometimes with unfortunate results of a collison; bruised flesh and scratched bikes. The path is clearly marked for runners with a paralell lane marked for bikes.
Bottom line is we should all be considerate of the other. Plain and simple.