How can Yahoo! beat Google at Search?

The key weapon - User Information  (gathered explicitly and implicitly as the user surfs Yahoo!'s large content network).  From the horse's mouth as per this NYTimes article, “Yahoo's two main advantages over Google - its vast array of original content and a database with information about its 133 million registered users. Knowing where searchers live and what their interests are, Yahoo believes, will let it present results that are more relevant and advertising that is more focused.”