The news today included a mention  of the NASA "robonaut" which is intended to begin to test the efficacy of using robots in space flight.  My experiences and interests in aviation has shown me that the human in the cockpit is both the limiting factor as well as the most expensive aspect of the aircraft.  I think that in space flight we would get a much greater return on our investment if we did not have to dedicate so much of the budget to transporting a human and keeping them alive with a significant margin of safety.  The additional monies available if humans were not included in the vehicle could be used for advancing robotics, artificial intelligence, remote control, communications and remote presence abilities.   While a human "on site" provides the most flexibility in terms of dealing with unexpected situations I think we can much more quickly field new technologies as well as much more cheaply without them (us).