[youeseh]

One possibility would be to build a more accurate social graph. So, let's say you have 500 friends on Facebook, but only 50 of those are people you speak to on a regular basis. This helps Facebook better understand your preferences based on your online interactions and the people who you associate with on a regular basis. You are the average of the 5 people who you spend the most time with, or something. This hopefully means that they'll be able to show you better ads.