'Pair programming' would get a bit frustrating, don't you think? I suppose productivity would greatly depend on the personalities involved.
I usually let who ever is "driving" just write the damn code. He might write poorer code than I, but we're just trying to solve story cards quickly and if the tests pass, I don't complain. I usually only perk up when I notice logical errors, or other places in the code that we'll have to change when my pair refactors something.
You're missing half the fun, then. Part of the point of code reviews (and pair programming is, at its core, extreme code reviewing) is make sure both write the best possible code, both in terms of being bug free and adhering to company standards.
If you don't care about how the code ends up in terms of structure other for the logical errors, you're doing it wrong (well, according to me anyway, so it's not that big of a deal :P)