A survey conducted by ExactTarget and cotweet asked Facebook users what they do and why.
43% of respondents say they are fans of at least one brand on Facebook. Of those users, the following reasons were the most common given:

Looking at this information, you might – as most companies do – immediately implement one of the first three reasons. You could offer a coupon or discount, encourage people to wear your brand like a badge, or give something away.
But I think this misses the point.
It’s the next two groups you should be paying the most attention to; people who want to know about the activities of your company and to get updates on future products.
These are the people who are giving your brand permission to talk to them.
Social media marketing is not a replacement for mass media. If you want broad awareness, you’re playing in the wrong sandbox. So when you create a Facebook strategy, don’t get stuck in the mindset of “most people want this, let’s give it to them.”
Instead, think about what the right kind of people want. The true fans.
Gather those people.