There's been a couple of interesting posts over at io9 recently about the future of the human race, with specific regards to space exploration. Humans are basically the limiting factor to space travel. We add weight and complexity because of our need to support relatively frail bodies. As we've seen, machines can make the trip to Mars just fine, but we're not sure humans could. So is the answer to adapt to space, instead of building space vehicles to support us, build bodies that can survive in space?
I think we'll get to a time when people do swap out parts for improved artificial versions, both in space and here on Earth. The question will be how we handle this from a psychological point of view. Does someone who has no biological body still count as human? If you remove all of hormonal drives and impulses, will you remove our humanity? How will removing the need/ability to procreate affect our society (it is, after all, the main driving force of our existence)?
These are big questions which will need to be addressed as the technology starts to appear and become more common-place. Initially it will probably be used to replace missing or damaged parts so there will be little debate, but when people are swapping biological bodies for mechanical ones, what then?