Forrester Research analyst Sucharita Mulpur interviewed 24 tech vendors on their experiences using Facebook for marketing and engagement:

A social-network presence, she found, was less effective at customer acquisition and retention than e-mail and paid search. The study found that the average Facebook metrics are a 1% click-through rate and a 2% conversion rate. E-mail marketing, by comparison, has an 11% click-through rate and a 4% average conversion rate. … Though companies theoretically show up on the news feed of their Facebook fans, the analyst said companies are unsure how frequently or prominently their posts do show up on the feeds. When retailers put like buttons on their product-detail pages, are they really thinking?” she said. “Your competitors can see what products are more liked than others. Are you exposing your sales information? So why would expose this information?”

Article from WSJ.