As I've said before, I think Kurzweil's focus on a singular A.I. is misguided... he's missed the target but hit the tree. Much of the exponential growth in technological progress (from the printing press to the Internet) has to do with improving the efficiency of information flow between individuals. I'm thinking that at some point this flow may approach neuronal levels of complexity and speed, at which point the collective intelligence of society (or groups in society) will tip over into something resembling a multi-human organism. It's hard to grasp now, but I doubt that whatever the Singularity ends up being will be easy to grasp at this pre-Singularity stage.

Arguing about brains in boxes just seems a little myopic to me.