According to an old roommate who went to an all male college in the deep south (where not one but two etiquette classes were required for graduation) the answer is as follows:
In the event the door is spinning before a lady is to enter, it is polite to let the woman go first.
In the event the door is stationary, a man should proceed first in order to start the door moving.
Either way you run the risk of an overzealous gent going too fast thereby tripping you in the pie!
Hope this sheds some light on an otherwise tricky etiquette problem : D