Having someone senior to me say my code sucks or being weighed down by a junior coder (in effect, training him) seems unpleasant.

Don't you ever do code reviews? Does someone then telling you how your code could be seem unpleasant, or does it actually help?

Pairing allows someone to do this in real time. It's not a senior/junior pairing - for pairing to really work well it's meant to be people of roughly equal skill. And counter-intuitive as it seems, any time we've tried it you tend to get more 'value' from it than from the two individuals coding alone.

Tony