One common complaint I hear from marketers is that social media is not (yet) a mass medium. For example, the circulation for Cosmopolitan is 3 million, while the magazine counts just 700,000 fans in Facebook. And while it seems (almost) everyone is creating, using or consuming social media today, it is a highly fractured channel. Thirty years ago, almost every person watching television was tuned into one of three networks; today, 550 million people use Facebook, and each and every one of them is their own network.

However, the fact that social media is fractured and personalized does not mean that it isn't a mass medium; it just means it is a challenging mass medium. Here is the evidence for social as a mass medium:

• Impressions: In a report published earlier this year, Josh Bernoff and I shared data developed using a new word-of-mouth analysis tool, Peer Influence Analysis. Forrester found that some 500 billion influence impressions about products and services are created in social media each year -- a number that is sure to grow when we repeat the research in 2011. That compares to around 2 trillion online ad impressions according to Nielsen (and which do people find more persuasive and worthy of attention -- ads or recommendations from friends?).