Great article by Rod Hilton on pair programming: http://www.nomachetejuggling.com/2009/02/21/i-love-pair-programming

When coding, the bottleneck is rarely typing speed. It's usually thinking speed. Pair programming tries to solve this by unleashing twice the brainpower on a problem. But it usually fails because most people (including me) take a very primitive view and think that the magic comes from simply putting two developers next to each other.

The magic requires more subtlety and structure, and Rod does a great job in describing it. This seems to be a common theme in XP Methodologies. They all sound simple, but practicing them well requires more thought than you would first expect.

Side note: On a scale of 1 to 10 for "names that sound like a pornstar", Rod Hilton gets an 8 or 9.