I've never experienced pair programming, and I'm dubious that I'd work well in it, but I'm amazed at employers that would prevent employees who were interested from working in pairs.
The best thing that comes out from it is the peer pressure to stay focused. Even if your pair doesn't know anything about programming, just having him sit there and watch you will make you at least twice as productive so that you don't end up reading Hacker News while your unit tests are running!
Sometimes we'll be so engrossed in the engineering, that neither of us will remember that restaurants close at 9pm and we have to stop to eat.
