8. A method comprising: receiving a search query; obtaining a plurality of search results for the search query from a search engine, wherein each search result identifies a respective search result resource, and wherein the plurality of search results includes one or more search results that identify search result resources that are in a particular site; using a site quality score for the particular site to rank the plurality of search results; categorizing as referring to the particular site each query that includes a site label identifying the particular site, wherein the site label is a term in the query that includes (i) an operator that identifies the term as a site label and (ii) a name of the particular site; and determining the site quality score for the particular site, comprising: determining a numerator that is a function of a first count of unique queries submitted to the search engine that have been categorized as referring to the particular site; determining a denominator that is a function of a second count of textually unique queries submitted to the search engine that have been associated with resources in the particular site; and determining the site quality score for the particular site as a ratio of the numerator and the denominator.
8. A method comprising: receiving a search query; obtaining a plurality of search results for the search query from a search engine, wherein each search result identifies a respective search result resource, and wherein the plurality of search results includes one or more search results that identify search result resources that are in a particular site; using a site quality score for the particular site to rank the plurality of search results; categorizing as referring to the particular site each query that includes a site label identifying the particular site, wherein the site label is a term in the query that includes (i) an operator that identifies the term as a site label and (ii) a name of the particular site; and determining the site quality score for the particular site, comprising: determining a numerator that is a function of a first count of unique queries submitted to the search engine that have been categorized as referring to the particular site; determining a denominator that is a function of a second count of textually unique queries submitted to the search engine that have been associated with resources in the particular site; and determining the site quality score for the particular site as a ratio of the numerator and the denominator. 9. The method of claim 8 , comprising: categorizing as referring to the particular site each query that includes a term that has been determined to be a term that refers to the particular site.