The internet has made is vastly easier for ordinary people to spread a message to other ordinary people. These "peer-to-peer" interactions are fast becoming a mainstay of online campaigning. "Consumers" have become almost completely desensitized to paid advertising, and quickly mass email is going the way of direct marketing postal mail. People are inundated with email and actively discard mass email messages without reading them, furthermore, advances in spam filtering can often block legitimate mass email.
The way to cut through these barriers is by having supporters contact their friends and family directly with your message.
This is often referred to as viral marketing. Web technologies can make it increasingly easy for people to spread a message, not just by forwarding it through their mail client, but using customized profiles on a website. This allows an organization (candidate or politician) to track which messages are the most compelling, how many people forward them (and to how many people) and how many of the second generation recipients click back through to the website and in turn forward the message.