1. A method performed by one or more computer systems, the method comprising: receiving a search query from a user; performing, based on the search query, a search of information regarding a corpus of documents to identify a ranked set of search results; identifying a first set of documents that are preferred by the user or a group of users; identifying a second set of documents that are different than the first set of documents, each document, in the second set of documents, being ranked higher than a threshold based on a global document ranking algorithm; generating an intersection set, documents included in the intersection set being common to both the first set and the second set; identifying at least one document, in the intersection set, that includes a link to a particular document in the ranked set of search results; re-ranking, based on at least one weight assigned to the at least one document, the particular document in the set of search results to obtain re-ranked search results; and providing the re-ranked search results to the user.