Google’s original breakthrough in search technology was to assess the value of a Web page according to how many other pages linked to it—an indirect measurement of how many people liked that page. Social networking offers another way to measure how many people think a page is worth looking at: examining which links users share with their friends.

While the pool of pages ranked through social networking will never be as comprehensive as that produced by Google, it has the advantage that it allows for more personalized search results. A person whose circle of friends shares a lot of sports-related content is more likely to be looking for information related to the Texas basketball team when searching for “Rockets” than someone whose friends like a lot of space-related topics.

With its hundreds of millions of users and its “Like” button, which lets users note which pages they like even while visiting other websites, Facebook is the leader in this new approach to indexing Web content (see “TR10: Social Indexing,” May/June 2011). In May, Microsoft started using data from Facebook to weight results from its search engine, Bing. Not to be left behind, Google recently added a “+1” button that allows users with public Google profiles to note pages that interest them and draws on this information to recommend pages to other users.