All significant development is done in pairs.
We have found that progress is faster, we can work longer without losing headway, and quality is higher. Typically the person types who has the best feel for where the code is going. It is as if the typist is crafting the individual methods, while the observer is monitoring strategy and tiny detail at the same time. We have found that with very little practice, most people adapt quickly to pair development. They get to like it, because progress is discernibly faster.