Did some pair programming this afternoon with Ken, on the Library project for the LPLUG. It really was amazing how much more can be accomplished with two programmers working together than the same two could produce working on their own.
Particular kudos to Schwern for the Test::More module, and particularly for is_deeply, which saved a HUGE amount of time and work on testing.
Also interesting is to see the looks that people give you when you're pair programming - like they think that you're just wasting half of your effort. I do know for sure that I always get more actual functional code written when I have someone working with me. Part of it is motivation. Part of it is the fresh ideas. Part of it is the catching of stupid mistakes before they can cause real damage. It's an interesting synergy.