1. A method comprising: receiving a search query, a plurality of generic search results, and a plurality of mobile search results, wherein the generic search results each satisfy the search query, identify a respective generic resource, and have a respective search result quality score, and wherein the mobile search results each satisfy the search query, identify a respective mobile resource, and have a respective search result quality score; determining that the search query came from a mobile user; evaluating, for each mobile search result in a set of one or more of the plurality of mobile search results, one or more properties of the respective mobile resource identified by the particular mobile search result, and modifying the particular mobile search result's respective quality score based at least partially on the one or more properties; wherein a first mobile search result in the set of mobile search results links to a mobile resource that links to downloadable content for a mobile device, and in which modifying the first mobile search result's respective quality score comprises increasing the respective quality score of the first mobile search result; and wherein receiving, determining and evaluating are performed by one or more data processing apparatuses.