I feel that pair programming is about discussing and solving your problem together rather than only sitting together on a computer, where one person is typing away and the other is plainly watching.
Of course, once you have a algorithm for you problem there is hardly any point sitting together but when you are still in the primitive stages of your solution I have experienced that it helps if two people are sitting together and charting out a roadmap to solve it.
I am still a beginner in this field so pardon me if I dont get the hang of pair programming the way its meant to be.