1. A computerized method for optimizing search result rankings obtained from a search result ranker, the method comprising: retrieving a first set of query-document pairs, each query-document pair of the first set having an associated post-impression features vector; generating a weight vector having a number of weights corresponding to a number of post-impression features in each of the post-impression features vector of the first set; generating a target function by using the weight vector and the post-impression features vectors of the first set; using a performance metric associated with the target function, optimizing the weights of the weight vector using the first set of query-document pairs to obtain an optimized target function; optimizing the search result ranker using the optimized target function; and using the optimized search result ranker to rank search results.