Have you ever wondered which other pages on the web link to your own? Wouldn’t it be nice to know which sites are talking about your content, and in which context? Well, a problem no more: now you can see all the backlink URL’s, post titles, and more right within the new Social reports .
announcement last month , and also take a look at in-depth example  of how to use these new reports to measure your user’s engagement in Google+.
Posted by Ilya Grigorik, Google Analytics team