1. A method comprising: receiving, by one or more computing systems, a request from a first user of a social network environment for a first structured document, wherein the social network environment comprises a social graph comprising a plurality of nodes and a plurality of edges connecting the nodes, each of the edges between two of the nodes representing a single degree of separation between them, the plurality of nodes comprising: a first user node corresponding to the first user; a plurality of second user nodes corresponding to a plurality of second users, respectively; a first concept node corresponding to the first structured document; and a plurality of second concept nodes corresponding to a plurality of second concepts, respectively; determining, by the one or more computing systems, a first data set that identifies one or more second concept nodes that correspond to one or more second structured documents, respectively, each second structured document being conceptually relevant to the first structure document corresponding to the first concept node requested by the first user, each second concept node in the first data set being identified at least in part on a relevance score for the second concept node in the first data set with respect to the first concept node calculated by the one or more processors based on connections in the social graph between the second concept node and the first concept node, each second concept node in the first data set having a relevance score greater than a threshold relevance score; determining, by the one or more computing systems, a second data set that identifies one or more second concept nodes in the first data set, each concept node in the second data set being connected by respective edges with the first concept node and one or more second user nodes that are each connected to the first user node; and selecting, by the one or more computing systems, one or more second concept nodes in the second data set to recommend to the first user responsive to the request.
9. The method of claim 1 , further comprising: generating, by the one or more computing systems, for each second concept node in the first data set, a score based at least in part on the number of user nodes connected to both the second concept node and the first concept node; wherein generating a score for each second concept node comprises (1) generating and (2) summing or otherwise combining: one or more coefficient scores between each second concept node in the first and second data sets and each of the user nodes connected with the user node corresponding to the first user; one or more coefficient scores between each second concept node in the first and second data sets and the node corresponding to the first user; one or more coefficient scores between each second concept node in the first and second data sets and the first concept node; or one or more coefficient scores between the node corresponding to the first user and each of the user nodes connected with a second concept node in the first and second data sets.