What is participtory advertising?

I've chosen for the theme of this semester's class, grassroots or consumer produced advertising. The image from the Dove soap web page serves as a current example where consumers are encouraged to create their own advertisements with the hope that they might be shown on network television or distributed virally via the web. There are myriad other examples from the upcoming Super Bowl to those consumer produced ads that now routinely appear on YouTube. We would expect mass marketers to be reluctant to give over so much power to consumers. However, by allowing consumers to produce commercials, marketing are creating potential allies, and while they may accede a certain amount of control, they maintain the power to negotiate the relationship with the consumer. Consumers who participate in such activies are considered "core" audiences because of the level of involvement required.