18. The system of claim 15 , wherein the plurality of similarities are based at least on a query competitiveness measured by a number of advertisers associated with search results for one of the pluralities of search queries.
15. A system, comprising: at least one computing device; and a network site classification engine in the at least one computing device, the network site classification engine comprising: logic that computes a plurality of similarities between a first plurality of search queries and individual ones of a second plurality of search queries, the first plurality of search queries returning an unclassified network site and the second plurality of search queries returning a plurality of classified network sites, individual ones of the classified network sites having a respective category, wherein the plurality of similarities are based at least on a query importance comprising a click through and the query importance is associated with a search query in the first plurality of search queries and the second plurality of search queries; and logic that classifies the unclassified network site into the respective category of one of the classified network sites based at least in part on the plurality of similarities.