In my short story, "Star Sheep Enterprise,." I had the colonists terraforming a new planet by using sheep to create viable soil.
This article from Slate, which I found Monday morning, talks about the very real problems of humans trying to adapt to an alien landscape. To wit: our gut microflora may not be able to exist on Martian soil.
It's a problem that scientists only just now seem to be getting their heads around. In the article, it's speculated that a lot of Western diseases like allergies and irritable bowel syndrome are caused because our diets don't expose us to the bacteria we actually need in order to keep our systems running properly. On Mars, those soil borne bacteria don't exist--or are replaced by chemical compounds dangerous to us.
Hydroponics are a short-term solution, and the "food pills" of old pulp fiction won't be a long-term fix, either, because our bodies need a very complex system of nutrition and cellular challlenges to keep them running properly--and none of this is well-understood, at the moment. Schlepping millions of tons of Earth soil to Mars would be cost-prohibitive, obviously.
So it may end up that yes, we humans can put a man on another planet...but we won't be able to keep him there for very long.