In my still on-going test with FB, Twitter & Gplus - I noticed that my website click throughs are higher when I post a new engaging article. The more interesting the articles are, the more Likes, Retweets & Shares I get. I also notice that some topics are more popular than others, so, when I notice a big jump in my stats, I make sure that I write more about that topic that created the boost - but not to the point of saturating my website with ONLY the popular topics. Also, whenever a topic gets re-tweets, the more traffic boost I get for my social media efforts.
Its a continued test but all worth the effort, makes me not to depend on Google search results anymore.