1. A method comprising the following computer-executable actions: accessing a data repository in a computing device, wherein the data repository comprises at least a first query and a second query issued by users of a search engine and search results selected by issuers of the first query and the second query; determining a first click distribution over the search results for the first query; determining a second click distribution over the search results for the second query; determining a measure of similarity between the first query and the second query based at least in part upon the determined first click distribution over the search results and the determined second click distribution over the search results; and labeling the first query and the second query as being similar queries based at least in part upon the determined measure of similarity between the first query and the second query.