Duncan Watts at Yahoo! Research has this to say -
A rare bunch of cool people just don't have that power. And when you test the way marketers say the world works, it falls apart. There's no there there.
Oh what then about a lot of poor souls who bet heavily on things to succeed hoping things will go viral, or that they are through by winning over the influencers? Interesting, because most things which became hugely popular, at least over the internet, owe their success to the viral power. More in this FastCompany article.