" . . .if you want to know why I might be reluctant to extend the graph of biological and economic growth over time, into the future and over the horizon of an AI that thinks at transistor speeds and invents self-replicating molecular nanofactories and improves its own source code . . ."

Machine intelligence has long been rated in raw speed of calculation. There is plenty of processing power available. If I handed AI researchers a computer an order of magnitude faster than what they were working on, their failures would certainly fail faster, which is an advantage, but there's no reason to think that they would necessarily be able to create an AGI immediately. If we knew how to code an AGI, we could do it today and run it on slower machines. Sure, it might take 10-100 times as long to think as machines that we will have in a few years, but that is irrelevant to displaying intelligent thought.

The main advantage of transistor technology is consistency, not speed -- Transistors don't forget. Absolute knowledge retention is the advantage that Deep Blue has over regular chess players. The speed element simply makes it possible for it to play chess at a speed that doesn't make humans bored.

Of course, it may be that human-like intelligence and creativity requires a sort of messiness. I worry that absolute precision and (human-style) creativity are somewhat incompatible, at least in a single entity. Undoubtedly, however, an AGI could at least be constructed that is much better at both than we are.