The problem is that our current economic system is not ready to deal with such a high productivity level. With technology advancements eliminating entire job classes virtually overnight, in our lifetime we will reach a point where there will be way more people than necessary jobs; and the economic system will have to adapt. Two simple (not easy) solutions that come to mind are artificial population control or a different resource diatribution model.
There's another solution: massive differentiation of the economy. I think this is already starting to happen (witness the success of YC). Entirely new categories of products and services are springing up, many of which are meeting plenty of demand. In the new wired world, information about these new products and services can travel fast enough for them to serve distributed clienteles; this makes them much more viable than they would have been as local businesses. In short, the long tail of business models has opened up. It is a time of mind-blowing opportunity, but the opportunities demand creativity. It's not enough to do what somebody else is doing; you have to find another workable point on the long tail.
I'm sure people thought like that when agriculture got automated and didn't need as many people any more. Higher productivity shifts people from industry to industry. There's often a lag between the death of one industry and the rise of another.
Just because it was true in the 19th and 20th century that human resources can reallocate from agriculture to manufacturing does not mean it will continue to be true in a future context.
Every day our R&D is chipping away at the necessity for a human labor force until we get to the day we have 0 percent employment.
