I think being a runner, you can't help but watch others run, when your not running. Be it in a car, on foot, or sitting in a pub. You see a runner go past, and you watch them. Its like your eyes are slowly drawn to them. Your looking at the gear they are wearing, what pace they are running, and guessing whether what level of runner they are.
Sometimes i have done this, and people think i am either eyeing them up or pouring scorn on them. But you can't help it. When running becomes part of your life, you do pay attention to other runners. It has also given me incentive to run, and think, yes, i could do with a run right now, wishing you were out there. On days when your feeling crap, and you see some overweight person struggling up a hill in their cottons, and you think, well if they can be bothered to get out there, why cant i.
There is something to be said for the past time of watching other runners, and not because i think they are hot!