Pair Programming Illuminated

is an excellent book by Laurie Williams and Robert Kessler. As usual I'm going to quote from a few pages

Programmers admit to working harder and smarter on programs because they do not want to let their partner down.

The pair results were also more consistent, while the individuals varied more about the mean. Individuals intermittently didn't hand in a program or handed it in late; pairs handed in their assignments on time.

Widespread use of pair programming involves a cultural shift in values of the organization - away from individual and toward team recognition and goals.

We have observed that effective pair programmers communicate with each other at least once a minute.

Interestingly enough, the more experience a developer has, the more likely he or she is to ask for help; novices are less likely to ask for help.

We used to consider a new person unproductive for their first three months. Now, we find that new people can help out almost immediately.

We still feel that a novice pair is a better alternative to a solo novice.

We believe pair programming is an integral part of XP, and it is dangerous to do XP without doing pair programming.