She opens the door and looks behind her. You make eye contact. Now she's required by our ridiculous office culture to hold the door for you. Except you're still, like, 10 yards away from the door. So you shuffle forward as quickly as you can. You can't run, because she'll tell you not to rush, and it'll be all awkward, like she inconvenienced you by holding the door for you. This whole little period is excruciating for a shy person.
This, like so many other things, was simpler in college. The culture at my school, at least, required nothing more than pushing your arm out while you walked through the door at your normal pace. If someone was behind you, they pushed their arm out for the next person. No looking behind you to see who's coming, no waiting for people. You could walk in a crowd of hundreds of people with barely any human interaction. Bliss!
The shuffle to walk through a door someone held for 30 painful seconds isn't the only "thing" about doors in my office. There's also an important decision to be made about thanking people. In order to exit my building, you have to walk through three doors in quick succession. I'm sorry, but I'm not thanking the same person for holding a door three times in 20 seconds. By the third time you sound like an idiot. I've adopted what seems to be the most popular pattern: I thank on the first and the last door.
Finally, you can judge a person by their door-holding technique. Holds the door back for you and gestures for you to enter before him (it's always a him)? Gentleman (and usually an Executive or someone in sales). Walks through the door and pushes his or her arm out to hold the door open behind them? Normal (this is by far the largest group). Walks through the door first and then stands there in the doorway holding it open behind them? Douchebag (and usually middle management).