well , it depends really i like to think of myself as a guru in this area, well i really am coz i studeid ecommerce bla bla.
anways to answer your question many companies seek the two way interaction with clients/customers on facebook. normally its hard/not feasible to have this in the offline world, but on facebook u can get ideas and responses from your market, how they like or dislike a new product, service et, if there are any complaints or praises, keeping them updated on upcoming projects, products etc.
it also sends the signal that you care for them, a good thing coz if they think u dont care about them, they gonna be running to your competitor.
forgive me, i think i am a little sloshed, am i making sense, this is embarrassing...