"In the study, which follows up on another report done last year by comScore called the Power of Like, the research firm found that being a fan of a brand on Facebook causes people to purchase that brand more frequently.

For example, comScore tracked people who were Starbucks fans on Facebook against a control group of people who weren't exposed to those messages. ComScore found that over a four-week period, fans and their friends bought 38% more frequently at Starbucks than people who weren't exposed to the Facebook marketing."