Eliezer -- To a first approximation, the economy as a whole is massively, embarrassingly, parallel. It doesn't matter if you have a few very fast computers or lots of very slow computers. Processing is processing and it doesn't matter if it is centralized or distributed. Anecdotal evidence for this abounds. The Apollo program involved hundreds of thousands of distributed human scale intelligences. And that was just one program in a highly distributed economy. We're going to take artificial intelligences and throw them at a huge number of problems: biology (heart attacks, cancer, strokes, alzheimer, HIV, ...), computers (cloud computing, ...), transportation, space, energy, ... In this economy, we don't care that 9 women can't produce a baby in a month. We want a gazillion babies, and we're gloriously happy that 9 women can produce 9 babies in 9 months.
Robin -- But Eliezer's basic question of whether the general models you propose are sufficient seems to remain an open question. For example, you suggest that simple jobs can be performed by simple computers leaving the complicated jobs to humans (at the current time). A more accurate view might be that employers spend insignificant amounts of money on computers (1% to 10% of the human's wages) in order to optimize the humans. Humans assisted by computers have highly accurate long term memories, and they are highly synchronized. New ideas developed by one human are rapidly transmitted throughout society. But humans remain sufficiently separated to maintain diversity.
So, what about a model where human processing is qualitatively different from computer processing, and we spend money on computers in order to augment the human processing. We spend a fixed fraction of a human's wages on auxillary computers to enhance that human. But that sorta sounds like the first phase of your models: human wages skyrocket along with productivity until machines become self-aware.
A welfare society doesn't seem unreasonable. Agriculture is a few percent of the U.S. economy. We're close to being able to pay a small number of people a lot of money to grow, process, and transport food and give the food away for free -- paid for by an overall tax on the economy. As manufacturing follows the path agriculture took over the past century and drops from being around 30% of our economy to 3%, we'll increasingly be able to give manufactured goods away for free -- paid for out of taxes on the research economy.