Re: I'm not a programmer
"I am a great proponent of brain-storming"
Then one of us has perhaps not really understood pair programming.
Brainstorming is a diversion from the normal day to day routine. When I was doing "pair programming" semi-officially, it *was* the normal day to day routine (it helps if you sit adjacent or have an electronic equivalent). As others have noted, PP is very dependent on compatibility, brainstorming less so (especially if a competent moderator makes sure everyone's voice is heard).
The project I was working on simply wouldn't have been delivered without the two of us - with different skill sets, different areas of knowledge, both of which were essential to the end product. Brainstorming as and when wouldn't have been anything like as effective, not least because once you've got an idea, you have to make it work, which pair programming can help with, whereas brainstorming isn't the right tool for making an idea work.