By way of example, last week I started a Facebook group for executives at independent online agencies. This is a very narrow audience in every sense of the phrase. I had two dozen friends from my list of connections that I invited to join the group. Those who accepted the invitation kicked off a viral effect that would be tough to turn off even if I wanted to. Their friends saw that they joined the group. Since independent agency executives know other independent agency executives, within a day I started getting requests from people I didn't even know to join the group.

Now, rather than doing some sort of expensive outbound communication (like a targeted email), I instead have qualified people coming to me. Apply these marketing principles to a for-profit endeavor and you've got a formula for launching targeted marketing programs that don't cost very much.