There's a website for M&M's where visitors can customize their M&M's to look just like them and then send the finished product to friends. The M&M's folks call this finding one's "inner M," and they say that so far, 1.5 million of these avatars have been created.

"Consumers are not creating content in order to pander, to posture to marketers," says Joseph Jaffe, who wrote "Life After the 30-Second Spot." "There's a degree of self-actualization."

Grant McCracken, a cultural anthropologist affiliated with MIT, says participatory advertising represents a "revolution" in thinking. It means marketers are actually "inviting" consumers "into the production of meaning," he says. "Just a few years ago people were still talking about trying to find and push the hot button inside the consumer."