1. A method of ranking documents in response to a search query comprising: retrieving previously stored user input regarding a relevance of a document to the search query; associating the previously stored user input with the search query and the document; determining a relevance formula having variables and parameters, the relevance formula for computing a relevance score for the document and the search query, wherein the variables comprise a plurality of features, and the parameters comprise a plurality of coefficients corresponding to each of the plurality of features; and ranking the document based on the relevance score, wherein the relevance score is dependent at least in part on the previously stored user input.