29. The system of claim 28 , wherein the search engine is operative to order the given item in the result set according to the ranking score for the given content item.
28. The system of claim 27 , wherein the search engine is operative to retrieve one or more content items in a result set in response to receipt of the query from the user; and the ranking engine is operative to determine a feature vector for a given content item in the result set, apply the ranking function to the feature vector for the given content item, and generate a ranking score for the given content item.