Here is an advocacy campaign to stop global warming that is using the friend of a friend (FOAF) to spread the message. Interestingly, i got an email about this that i think was not sent through the website, but someone just sent me an email about it....

[l:http://www.stopglobalwarming.org/campaigns/sgw/register/8b5895076e66f6363237564fc5e38e8d|You can go to my page on the system]