If you're looking to get a coupon for the facebook advertising system, check out the link above for more information. Facebook ads allow for some very interesting demographic targeting settings, where one can limit an ad's exposure to members of a certain sex, age, and interest. This can prove to be a more effective way of "getting in front of your audience" when compared to something like television advertising, where you might have to shoot for a broad demographic that a particular show and/or network might attract.
Also, with total members numbering possibly as high as 700-750 million (and counting, still), there's obviously a large potential pool of people to whom to serve your ads. Also, given the nature of the platform, a good number who try facebook will keep using it, and so that allows for repeated ad impressions.