8. A method of providing search results responsive to search queries, comprising: at a server system: receiving from client devices user hover periods associated with a plurality of search results which correspond to multiple search queries, a respective user hover period comprising information about a length of time that a user hovers a user-controlled pointer over a display region occupied by a respective search result of the plurality of search results without user selection of the respective search result; updating relevancy values of the search results at least partially in accordance with their respective user hover periods; and in response to a search query after the update of the relevancy values, identifying a set of search results for the search query in accordance with their relevancy values, the set of search results including at least one search result whose respective relevancy value has been updated.
9. The method of claim 8 , wherein updating relevancy values includes: retrieving impression data associated with the plurality of search results provided to the client devices in response to the search queries, wherein the impression data comprises data identifying how many times and in what order the search results in the plurality of search results have been provided to the client devices in response to the search queries; receiving from at least a subset of the client devices the client attention data, the client attention data including the user hover period associated with search result if the hover period is greater than a threshold value; and updating the relevancy values for at least a subset of the plurality of search results in accordance with their respective impression data and client attention data.