7. The system of claim 6 , wherein the tracking component is further operable to store click data that comprises, for each user click made by any of the multiple users of the client system and not by other users of the search engine on a search result presented in response to a search query, (iii) data representing how much time a respective user spent on a corresponding document result.
6. The system of claim 5 , wherein the tracking component is operable to store click data that comprises, for each user click made by any of the multiple users of the client system and not by other users of the search engine on a search result presented in response to a search query, (i) the search query corresponding to the user click, and (ii) data identifying the search result corresponding to the user click.