Topic: Opinions on Pair Programming?

My organization is running a pilot project using pair programming so we can learn more about it and to figure out if it would be a good fit for our organization. The developers so far have mostly praises for the practice, and as a ScrumMaster, I've seen benefits that range from lower issue counts to the ability to continue on when we loose one developer due to a family emergency (I know, that's not following the pure pair programming practice of if one member of the team is gone, the other member does something else until they return, but we still had value from the practice since the remaining team member knew what needed to be done and could carry on.).

Our product manager is not so sold on pair programming. He sees it as a loss of productivity, since we have 2 developers now working on the same set of code. He's not sure that it will help reduce testing time (since there should be fewer issues), and while the theory of reduced maintenance (because of fewer issues released in production) sounds nice….he's worried about the here and now. We've only been in this pilot for 7 weeks….so it hasn't been very long.

Thus, I'm interested in hearing any opinions and/or experiences the forum may have had with pair programming. What pros and cons did you experience? Any words of wisdom in dealing with a product manager who may not know enough of the practice to fully understand the hoped for benefit….and does not have the patience to find out?