Methods, apparatuses, and computer-readable media for serving annotations are disclosed. When a contact of a user recommends an ad, the score of the ad may be boosted in an ad auction. The amount of boosting depends on contact affinity. Contacts with greater contact affinity may be more influential, and ads that are recommended by such contacts may have a higher click-through rate. The greater the affinity between the user and contact, the greater the boost to the ad score. Affinity may be measured by a weight value, which is determined by, for example, social network interactions, e-mail/instant messaging communications, and phone logs and contact lists.