Since Scott has brought the Worldchanging community to our attention, let me explain--from the perspective of a sympathizer and cheerleader--some of its cool features, in no particular order. (Keep in mind that some would likely debate my stronger claims. They're just my own biased perceptions as a person who has been enthusiastically watching the group since its launch in 2003.) I strongly suggest starting by reading the very short "about" blurb on their site.
Worldchanging is a movement that aims, step by step, to actualize the fair, robust, and sustainable human civilization that now exists only in potential. And when they say "potential", they mean it. In fact, they don't even say "potential"; they say "it's here" already, and that we need only "to put the pieces together".
Worldchangers see the present political, economic, and social moment as a battleground on which a high-stakes, "all-or-nothing" (to use Steffen's words) battle is transpiring for the continuation of human life as we probably want to live it (unless we have a deranged idea of "the good life"). We either fail to put those pieces together (in which case the world falls into deeper and deeper turmoil), or we actually succeed. The prize for success could be about as close to utopia as we can get. The struggle for sustainable polyculture and more efficient industry is merely one facet of what Steffen (who I also had the pleasure of meeting recently), in the same piece referenced above, labels as the larger "fabric" of plights that challenge us now: climate, biodiversity, population, poverty, conflict, public health, toxics, terrorism.
In the face of this great struggle, it's all too easy to fall into the trap of nostalgia. "Technology is ripping the world apart! Let's reject all technology and restore our civilization to 'the natural order'!" This kind of bleak, depressing reminiscence of the past is known (to some of us) as "dark green environmentalism". The color of Worldchanging is--you guessed it--bright green! Worldchangers don't conflate (as many environmentalists make the mistake of doing) the insensitive, exploitative technodevelopment of the past with the potentially globe-renewing technoscience of the present and future. For me, that's a great reason to embrace Worldchanging.