1. A computer-implemented method comprising: hosting, using one or more computing devices, a social network comprising a plurality of communities associated with a plurality of users; identifying, from the plurality of communities, a set of communities that a first user belongs to; determining, using the one or more computing devices, a list of classifications for the first user based upon the set of communities; determining a degree of personalization based on an amount that the first user has participated in each community of the set of communities; determining, using the one or more computing devices, personalization information from the list of classifications associated with the first user and the degree of personalization; generating, using the one or more computing devices, a personalized search query based upon the personalization information; and searching, using the one or more computing devices, a content index using the personalized search query to produce a search result set comprising documents relevant to the personalized search query.