in reply to Tricking Our Egos
If you've ever worked with a smart programmer looking over your shoulder as you code, you may find later that his or her presence sticks around far longer than the actual person. I had an extremely good experience coding/designing/documenting closely with another programmer for only a week and find that, when needed, I can call him up to sit on my shoulder (like those angel vs. devil images) and tell me how to work through a problem or untangle a knotted design.
(That sounds kind of weird. It's not, really, just a form of talking to the cat or thinking yourself to have a fever just to say out loud what you're thinking.)
I think XP's reliance on pair programming is one of its most attractive features. Even if it's one of the most difficult to implement since many people think of their code as art that can't be defiled.