I don't have much experience with pair programming in general, but I have some in pair debugging. And in my experience, for a difficult debugging problem this

I don't have much experience with pair programming in general, but I have some in pair debugging. And in my experience, for a difficult debugging problem this pair debugging is a very powerful tool. It is hard to measure, of course, but I have strong feeling that the productivity of a pair is way more than a sum of individual productivity in such cases. I've seen bugs identified and fixed in hours, where both of the paired programmers believed it would take them days to fix if working alone.