In a recent post for the Foresight Institute, AI researcher J. Storrs Hall talks about the four different kinds of AI that might eventually surpass humans as planetary overlords. But he's not worried:
The key thing to remember when thinking about the economic AI takeover is that it is not something we should be trying to prevent. Why shouldn't we, the human race as a whole, build machines to do the hard work we need done, and spend our time enjoying the resulting wealth? Why shouldn't we spend our efforts deciding what needs to be done, and let the machines do it
Sounds very Asimovian.