Facebook made waves when it revealed that it was optimizing the News Feed to make brand Page content less likely to reach fans without some kind of paid support. Advertisers were understandably frustrated. After all, one of the primary objectives of social media marketing was to increase fans, so that the brand could then share content with them organically. The time for growing fans to deliver what was essentially free advertising has come to an end.
This is a very good thing. The future is bright for social media marketing because it's success is now defined by what all elements of the marketing mix are: reach, awareness, click-through, brand lift, sales, purchase intent and beyond.
Fans, likes, retweets, comments, shares and other metrics that have come about in the age of social media marketing are all vanity metrics until marketers can answer what they indicate and why they're important to measure.