It’s EarthDay, and Mashable magazine – an invaluable resource for anyone interested in social networking technology and developments – have a useful article, by Elsa Wenzel, on how various activist organisations are harnessing the power of social networks, either using existing platforms like Facebook, or developing their own dedicated networks.

A more extensive list is provided by William Slawski at SEObythesea. Amongst the sites covered is GreenVoice.com which I particularly like.

Greenvoice - a social network for environmental action