12. The system of claim 11 , wherein updating relevancy values includes: instructions for 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; instructions for 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 instructions for 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.
12. The system of claim 11 , wherein updating relevancy values includes: instructions for 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; instructions for 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 instructions for 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. 13. The system of claim 12 , wherein the updating the relevancy values includes: instructions for generating at least one client attention coefficient for each of the search results in the subset in accordance with the impression data and the client attention data corresponding to the search results; instructions for combining the at least one client attention coefficient associated with each search result in the subset with at least one other query-independent metric of the search result's importance or popularity; and instructions for generating a relevancy value for each search result in the subset in accordance with its combined client attention coefficients and the at least one other query-independent metric of the search item's importance or popularity.