The social engagement tracking in Google Analytics is great. Google +1 works by default if you use the +1 Button Creator. However, one needs to do a bit of configuration to get tracking working for other things like Twitter tweets and Facebook likes. The popular WordPress plugins for Addthis and Sharethis use Google Analytics Events for tracking social engagement rather than the newer _trackSocial method. So, for the time being, if you want to get track social engagement with Google Analytics social reports, you’ll need to add your own code. Don’t be alarmed though, it isn’t all that difficult. This step by step guide about Tracking Social Engagement with Google Analytics will get you headed in the right direction.
One thing that wasn’t clear (to me at least) was were the javascript code should go for the Twitter event binding. This is important when considering a blog index page where there are multiple tweet buttons on the page that are associated with different posts. Twitter’s code handles this quite well, so long as you put the call to twttr.events.bind and the function extractParamFromUri somewhere where they only get called once. In my case, I created a .js file for these two things, which loads in the header along with widgets.js.