Pair Programming
Simon Baker has a nice entry defending pair programming. If you are among the many who find agile methodologies appealing, except for this one quite controversial quirk, you should read it.
I agree with most of his conclusions. Pair programming is not for everyone, but rather than being a matter of introversion versus extroversion, it depends on people being willing to let go of their ego and their need to hide mistakes until they have been fixed. Exposing the way you work is something that some simply refuse. Perhaps they were brought up with lots of praise..