Google should worry about this: More people are discovering content through social networks than through search.
Anyone that had a website a few years ago knows well that most traffic use to come via Google. This has changed. As the chart shows, more traffic is being referred by social networks than by search engines.
People trust recommendations from people they know more than any machine search algorithm. As this becomes the way people finds new stuff, advertisers are going to be more and more interested in Social Networks.
Search will not disappear nor Facebook will kill Google. However in “organizing the World’s information”, in particular the one that matters to you, the people you trust are a big part of the story. Facebook seems to be organizing that better than Google.