I doubt we can terraform Mars. We might be able to, one day, but for the time being we will be living in nice cozy pressure domes. The same, but to an even greater extent applies to the Moon, of course.
While I am heartily envious of all the people who get to play with robotic vehicles on different planets and get paid for it as well, I do not think humans have a place in space for a very, very long time to come. And with that I mean centuries, not decades. I think the plans of the Bush administration to go to Mars by 2020 or thereabouts are too ambitious, to the point of plain insanity. Space is simply too hostile for humans, and we do not have the technology, nor the social skills to pull it off. I say we forget about venturing out into space further than the Moon, until we have figured out a decent engine, learned to live together peacefully on Earth without religious nuts threatening to blow us up in the name of God or Allah, and worked out what exactly it is we want to do in space. As long as the answer to 'why?' is 'because it's there', we are doomed to fail: mountains could be conquered that way, space can not.