@cockswain – I wholeheartedly agree. :)
I was looking for an email forward I got eons ago, where a professor asked students this question and one of them replied that when one person yawned, it created an air pressure disturbance, which then caused other people to yawn to accomodate the change in pressure. I always liked that answer and kind of wish it was true.
Anyway, in searching for that, I found this article suggesting that we yawn to cool our brains down and there’s another article that.says how cool our brains are will affect our susceptibility to catching someone else’s yawn.
I have perfected the art of yawning with my mouth closed (to prevent socially inappropriate yawning), but my technique involves breathing in a lot of air through my nose and then back out. So the brain-cooling thing jives, considering nose-breathers have a lower incidence of catching yawns (as well as people with cool packs on their foreheads).