The nice thing about bamboo is that it grows quickly and can be replenished easily. In other words, it is a very renewable resource. I have a friend who will not knit with animal fibers because she thinks it is cruel (I don't agree with her, but she's entitled to her opinion). She only knits with synthetics, cotton and ...... BAMBOO. Anyway, she says it costs more, but she sees it as more earth/nature friendly.
Course, what we need is for Target to carry the Bamboo yarn, then we'd be set.