Stairwell Etiquette

Alright... this has been bugging me for some time. It happens to everyone, all the time. I have generally good manners, and I am the sort of fellow that will wait to hold a door open for someone, especially the elderly.
What happens if, you are on a stairwell. One of those nice ones that is half and half. If you are at the halfway landing and the other person is just entering the stairwell, should you wait and hold the door open? Should you rush up the last half of the stairs so you don't need to?
If you are at the door to the Post Office, what is an acceptable distance for another person to be away from you for you to NOT hold the door open? 10 yards? 5 yards? You can easily get trapped into being "Jeeves the Postal Butler" if you set this distance too far....
Back to the stairs. If you enter the stairwell after holding the door open to allow another person through, should you wait a few seconds before following them up or down the stairs? Maybe ride real close in case their personal distance fo rdoor holding is only 2 feet...?
Sheesh, these things just bug the hell out of me... Next time someone doesn't say thanks, I'm gonna push by the person, let a ripper go and bolt up the stairs as fast as I can, shouting "Catch this lardo...."