11. A system comprising: a profile store containing a profile for each of a plurality of users of a social networking system, each profile identifying a connection to each of a plurality of other users of the social networking system, the plurality of users comprising a plurality of viewing users; an action logger for logging information, by a social networking computer system, related to actions taken by the other users of the social networking system who have a connection to the viewing users; an advertisement request database for storing, by the social networking computer system, a plurality of advertisement requests from advertisers to the social networking system to sponsor stories for display to the viewing users, each advertisement request indicating: a type of action by other users with whom the viewing users have connections, the type of action selectable by the advertiser from a plurality of types of actions provided to the advertiser by the social networking system, and an instruction to provide messages to the viewing users that the other users connected to the viewing users in the social networking system have performed actions of the indicated type of action, wherein a bid amount for the advertiser to sponsor stories that match the advertisement request to accelerate the sponsored stories such that the sponsored stories are published in a news feed though at least some of the stories would not have otherwise been selected for publication without sponsorship; a newsfeed generator for generating, for each of the viewing users by the social networking computer system, based on the logged information, a set of stories that is personalized for the viewing user such that each viewing user has a different set of stories, each story comprising information about at least one of the actions taken by a user of the social networking system who has a connection to the viewing user; a social networking computer system advertising server capable of receiving advertisement requests to sponsor stories for display on the social networking system, the advertising server configured to, for each of the viewing users, using the logged information and the indicated type of action in an advertisement request to match the advertisement request to one or more of stories to identify stories for sponsorship based on the story comprising: an action that corresponds to the type of action identified in the advertisement request, and the action having been taken by another user of the social networking system who has a connection to the viewing user, the advertising server further configured for: computing, by the social networking computer system, an affinity score between the viewing user and at least some of the generated stories, the affinity score for each of the stories based on the viewing user's affinity for the user who took the action described in the story, and selecting, by the social networking computer system, stories for display in a user interface for the viewing user, the selected stories comprising: (1) a set of stories identified based on the affinity scores indicating affinity for the story above a threshold level, and (2) one or more of the stories identified for sponsorship, the stories identified for sponsorship having been accelerated relative to others of the stories generated based on the bid amount, and generating a news feed customized for the viewing user that includes the one or more of the stories identified for sponsorship interspersed with the selected set of stories; and a social networking computer system web server configured to provide for display in user interfaces for each of the viewing users the generated news feed that is customized for the viewing user such that different stories are included in the news feed for different viewing users.
11. A system comprising: a profile store containing a profile for each of a plurality of users of a social networking system, each profile identifying a connection to each of a plurality of other users of the social networking system, the plurality of users comprising a plurality of viewing users; an action logger for logging information, by a social networking computer system, related to actions taken by the other users of the social networking system who have a connection to the viewing users; an advertisement request database for storing, by the social networking computer system, a plurality of advertisement requests from advertisers to the social networking system to sponsor stories for display to the viewing users, each advertisement request indicating: a type of action by other users with whom the viewing users have connections, the type of action selectable by the advertiser from a plurality of types of actions provided to the advertiser by the social networking system, and an instruction to provide messages to the viewing users that the other users connected to the viewing users in the social networking system have performed actions of the indicated type of action, wherein a bid amount for the advertiser to sponsor stories that match the advertisement request to accelerate the sponsored stories such that the sponsored stories are published in a news feed though at least some of the stories would not have otherwise been selected for publication without sponsorship; a newsfeed generator for generating, for each of the viewing users by the social networking computer system, based on the logged information, a set of stories that is personalized for the viewing user such that each viewing user has a different set of stories, each story comprising information about at least one of the actions taken by a user of the social networking system who has a connection to the viewing user; a social networking computer system advertising server capable of receiving advertisement requests to sponsor stories for display on the social networking system, the advertising server configured to, for each of the viewing users, using the logged information and the indicated type of action in an advertisement request to match the advertisement request to one or more of stories to identify stories for sponsorship based on the story comprising: an action that corresponds to the type of action identified in the advertisement request, and the action having been taken by another user of the social networking system who has a connection to the viewing user, the advertising server further configured for: computing, by the social networking computer system, an affinity score between the viewing user and at least some of the generated stories, the affinity score for each of the stories based on the viewing user's affinity for the user who took the action described in the story, and selecting, by the social networking computer system, stories for display in a user interface for the viewing user, the selected stories comprising: (1) a set of stories identified based on the affinity scores indicating affinity for the story above a threshold level, and (2) one or more of the stories identified for sponsorship, the stories identified for sponsorship having been accelerated relative to others of the stories generated based on the bid amount, and generating a news feed customized for the viewing user that includes the one or more of the stories identified for sponsorship interspersed with the selected set of stories; and a social networking computer system web server configured to provide for display in user interfaces for each of the viewing users the generated news feed that is customized for the viewing user such that different stories are included in the news feed for different viewing users. 15. The system of claim 11 , wherein each of the set of stories personalized for a viewing user communicates an action performed by another user of the social networking system who has a connection to the viewing user, wherein the action is communicated to the social networking system and is not directly observed by the social networking system.