1. A computer-implemented method for processing search results, comprising: receiving a search request against a corpus of documents, wherein the search request specifies one or more search terms; generating an initial set of search results, wherein the initial set of search results identifies a plurality of documents responsive to the search request, ranked in an initial ordering, and wherein each of the plurality of documents contains text; receiving user indication of: (i) at least one document relevant to the one or more search terms and (ii) at least one document irrelevant to the one or more search terms; by operation of one or more computer processors, training a new statistical classifier using each relevant document as a positive training example to form a first category of documents recognized by the statistical classifier and using each irrelevant document as a negative training example to form a second category of documents recognized by the statistical classifier, wherein the at least one relevant document and the at least one irrelevant document form a training set for the new statistical classifier; supplying each document in the initial set of search results and not in the training set, to the trained statistical classifier to obtain a measure of similarity between the respective document and at least one of the categories recognized by the trained statistical classifier; supplying one or more documents from the corpus and not included in the set of initial search results, to the trained statistical classifier to obtain a measure of similarity between each of the one or more documents and at least one of the categories recognized by the trained statistical classifier; re-ranking the initial set of search results based on the measures of similarity obtained from the trained statistical classifier, comprising ranking each document having a measure of similarity to the first category of documents that exceeds a first user-configurable threshold, ahead of each document having a measure of similarity to the second category of documents that exceeds a second user-configurable threshold; and outputting the re-ranked search results for display to a user.