Wood, at least as far as flooring goes, is not a particularly renewable material. It takes centuries for a forest to regrow -- it might as well take forever, for all the damage done to Earth through harmful harvesting methods and deforestation.
Bamboo, on the other hand, grows like a weed -- at eight times the rate of hardwood, to be exact. It's extremely renewable, not just because of the growth speed, but also because when bamboo is harvested, the plant doesn't die. It just grows back, and quickly, making it an excellent green option for floors.
It's at least as hard and stable as most hardwoods, often more so, and it typically doesn't dent as easily as hardwood floors. Pricewise, they're pretty comparable.
Floors are just one area for bamboo. It also makes a great countertop, butcher block and cabinet material. Bamboo rugs are big. Artists use it in furniture, too.