20. A computer-implemented method of providing a search result set relevant to a search query, the method comprising: hosting a social network comprising a plurality of communities, each community having a plurality of users; storing a user profile for each user including a first user and a second user, the user profile identifying the user's membership in at least one of the communities; receiving the search query directed to a content index that is independent of the social network from the first user who is a member of at least one of the communities; determining personalization information including a first search phrase and a second search phrase, the first search phrase being determined from the first user's user profile and data from the second user's user profile, the second user's user profile having a degree of separation from the first user's user profile in the social network, and the second search phrase being based at least in part on the first user's membership in the at least one of the communities and a level of personalization selected by the first user for personalizing the search query received from the first user, wherein the level of personalization indicates a total number of the communities from which the second search phrase is retrieved; combining the search query received from the first user and the first search phrase and the second search phrase to form a personalized search query; and searching the content index using the personalized search query to produce the search result set comprising documents relevant to the personalized search query.
21. The method of claim 20 , wherein determining personalization information including the first search phrase further comprises identifying a classification of the at least one community.