The internet has proven itself to be the most effective way at informing people about issues that matter to them. Once people are informed, they want to act -- and many times the appropriate action is to let another person or organization your support for a position.
This website is a free service offered to users of the Internet to collect and organize signatures on a petition. It uses the standard "interpret this image" challenge to insure that the petition is being signed by a human. By packaging the signing activity into one frequently used service, all of the standard pitfalls that activists could fall into are avoided.
Similar, even more sophisticated services for accepting donations on behalf of an organization or cause, are also available on the web. Both of these services allow the activist to concentrate on informing people about the issue at hand, and to not have to worry about the mechanisms for achieving a mass effect in support of the issue.