Facebook is, at the core, an entertainment destination where people connect. That’s the primary goal anyway for the average Facebook user, but there are plenty of ways to interact with companies as well. A new study by ExactTarget and CoTweet finds that one of the key drivers to get a Facebook user to “like” a brand is to offer a coupon or a discount in exchange for fandom.

With “64% of all U.S. consumers, and three quarters of Millennials” creating a profile on Facebook, it has now become the “default” social community and a great place for brands to connect directly with their consumers. But half of those users only “like” between one and four brands. The most direct route to their fan box is through any special offer. According to the study, 40% of the respondents were prompted to like a brand based on an offer for a discount or promotion, even for a promised upcoming sale or coupon.

The other primary motivator to like a company or brand on Facebook, however, is simply to publicly display affinity for a brand to friends. It’s an endorsement that is motivated primarily by affection for the brand.

So what can you offer to your potential fans? How do you attract the attention of your brand advocates? Can you afford to miss out on the average Facebook fan who provides a brand $136.38/year (which can optimally fluctuate to $270.77)? What are you doing to attract attention on the default social community?