A basic premise of Web 2.0--social networking--is that certain tools and techniques become more valuable the more people use them. When only a few people had email, you couldn't count on reaching anyone and its uses were limited. Once it became widespread--a default option--the possibilities and importance increased. Facebook, MySpace, Ebay, Twitter--all examples illustrating this expansion.
Greenies and environmental groups have been trying to figure out how to operate through these new media; Grist, for instance, is doing a great job building communities around environmental issues. A somewhat newer initiative is WiserEarth, which has some unique features, including map-based searching that identifies groups and agencies in a particular area. Enter your zipcode, for instance, and there's a Googlemap pinpointing, by street address, a whole range of activist institutions. WiserEarth also has interest-areas and discussion groups that allow you to follow out topics, connect with others and learn as you go. It's a Creative Commons initiative, so open to all. It should be better known, larger and more valuable.