In college, I learned about new music from my friends. Like it or not, I picked up tips about personal style from them, too. You can blame them for some of the looks I've sported through time. The important point here is that my market-facing tendencies are not defined by my age, race, or socio-economic status as much as they are by the people I hang out with. This is why word-of-mouth marketing is so powerful.
If you really want to sell something, get people to start telling their friends about it - get people excited enough to want to tell their friend about it. Much has been made of the micro-demographic data that Facebook can provide. You can determine much about a person by looking at their Facebook activity. How cool is it to be able to segment an audience by knowing that they are within an age bracket, like the Daily Show, listen to Muse, and like to cook? I can't really think of the exact product you'd sell that audience, but you can get a pretty specific picture of a person by looking at their likes and activities. That's how the traditional thinking goes.
First, break your customer base down into units as small and clearly-defined as possible. Next, choose the segment that's most likely to respond to your marketing efforts. Then, choose a tactic (promotion, spokesperson, attitude) that you believe resonates with that group. Then, measure your success and adjust tactics if necessary. If you're lucky, you get it right and you sell a lot of product. If not, rinse and repeat.
That process seems a little old school in today's world. That process is based on broadcast thinking. Broadcast is a one-to-many channel (like network TV or print) where a single source holds the key to reaching your target audience. You had to depend on agency analysis of who was watching or reading what so that you could adjust your marketing tactics. In today's world, much of the content distribution is shared between friends or even generated by the individuals. In today's world, you have platforms rather than channels.
Facebook is a perfect example of just such a platform. The number of active users is closing in on the population of Europe. These users share thoughts, preferences, and entertainment content with each other. It's a pretty good bet that the content they share will resonate with some number of their Facebook friends. It seems like a no-brainer to overlay marketing efforts on top of this sharing. To be fair, those little ads on the right are supposed to be targeting you as a user but, at least for me, they don't quite seem to have me figured out yet. I would suggest a more direct approach.
Users can already tag other Facebook users in the photos they upload. However, in flipping through the photos posted by me and my friends, there are quite a few products in the photos as well. Why not let users tag products (clothes, for example) in their photos. When their friends click on those tags, they could be directed to a site where they can view the products. If they like them enough, they could purchase them. It would be easy enough to pass a token for the Facebook user that referred the product, and give them a little something-something for the effort.
In effect, you're creating very specific spokespeople. You can have one spokesperson who resonates with 1,000,000 people, or you can have 100 spokespeople who resonate with 100 people each, who in turn then resonate with another 100 people. Either way, you get the same reach, but you can achieve the latter without big endorsement contracts and media spends.