18. A system for determining a classification for a query, the system comprising: one or more servers; an interface to the one or more servers configured to receive a request to determine whether to assign a classification to a first query; a search entity classifier engine installed on the one or more servers that is configured to select a plurality of search entities that are associated with the first query based on respective user behavior data for the first query associated with each of the search entities; and a query classifier engine installed on the one or more servers that is configured to: determine a first measure of how many of the plurality of search that have been assigned the classification; determine that the first measure of how many of the plurality of search entities have been assigned the classification satisfies a classification threshold; in response to determining that the first measure of how many of the plurality of search entities have been assigned the classification satisfies the classification threshold, determine a second measure of how many of a top group of search entities from the plurality of search entities have been assigned the classification, each search entity in the top group of search entities being in a subset of the plurality of search entities having highest respective measures of relevance to the query based on the user behavior data; determine that the first measure of how many of the plurality of search entities have been assigned the classification is consistent with the second measure of how many of the top group of search entities have been assigned the classification; and in response to determining that the first measure of how many of the plurality of search entities have been assigned the classification is consistent with the second measure of how many of the top group of search entities have been assigned the classification, assign the classification to the first query.
18. A system for determining a classification for a query, the system comprising: one or more servers; an interface to the one or more servers configured to receive a request to determine whether to assign a classification to a first query; a search entity classifier engine installed on the one or more servers that is configured to select a plurality of search entities that are associated with the first query based on respective user behavior data for the first query associated with each of the search entities; and a query classifier engine installed on the one or more servers that is configured to: determine a first measure of how many of the plurality of search that have been assigned the classification; determine that the first measure of how many of the plurality of search entities have been assigned the classification satisfies a classification threshold; in response to determining that the first measure of how many of the plurality of search entities have been assigned the classification satisfies the classification threshold, determine a second measure of how many of a top group of search entities from the plurality of search entities have been assigned the classification, each search entity in the top group of search entities being in a subset of the plurality of search entities having highest respective measures of relevance to the query based on the user behavior data; determine that the first measure of how many of the plurality of search entities have been assigned the classification is consistent with the second measure of how many of the top group of search entities have been assigned the classification; and in response to determining that the first measure of how many of the plurality of search entities have been assigned the classification is consistent with the second measure of how many of the top group of search entities have been assigned the classification, assign the classification to the first query. 20. The system of claim 18 , wherein the plurality of identified search entities comprises a plurality of sites, and wherein the respective user behavior data associated with each site of the plurality of sites represents user behavior relative to one or more documents on the site when the one or more documents were provided as search results for the first query.