1. A method performed by one or more computers, the method comprising: receiving, at a server system, data indicating a first user's rating for a content item; storing, by the server system, data that associates the first user's rating with the content item; receiving, by the server system, a search query from a device associated with a second user; and providing, by the server system, search results in response to the search query, the search results indicating the content item and one or more other content items, wherein the search results are selected or ranked based at least in part on the first user's rating for the content item and ratings that other users provided for the content item.
14. The method of claim 1 , wherein providing the search results comprises providing search results indicating content items selected based at least in part on (i) a friend list that indicates friends of the second user and (ii) ratings for content items provided by the friends of the second user that are identified in the friend list.