An Observation
People seem really surprised when I hold a door for them. I mean to hold it a second while someone catches up to you is one thing, but if someone is coming towards you or if you hold a door and let someone go through ahead of you, they seem really confused for a second, then you'll hear one of the most genuine "thank you"s you've heard in a while. It's kind of incredible, really. And even if someone isn't pleased about it (though I've not yet observed anyone to be displeased) at least you've confused them a bit, which is nearly as good.
I'm surprised there isn't more door-holding going on here, with the volume of military folk here. What happened to the day when a serviceman (at least when he was in formals) was a gentleman?