Influencers and the new agency model

I heard an interesting presentation by Paul Gillin tonight at the Delta Chelsea for Canada's next top ad exec. Paul is a writer and media consultant specializing in information technology topics. Tonight, he focused on a topic dear to my heart-- the viral video. Diet Coke and Mentos, millions of viewers and not a penny spent by the Coca-Cola Company. A small company called BlendTech that makes commercial blenders realizing a 500% increase in sales after starting to show Youtube videos of the company founder blending iPods, garden tools, golf balls, and fifty other neat things. The interesting thing here, and I think the message Paul was trying to get across to this ballroom full of marketers, is that your customers control your brand and joining the conversation is the most effective way to market to this new savvy consumer. --The part I still can't really figure out is how agencies can make money in this environment? Typically agencies are making a percentage of media buy, or a creative retainer, but when the brand marketers can spend no money and get ten million eyeballs how does the new agency model work. I'd love a comment?