I was finally able to find some good statistics on share buttons.
This article by Fast Company gives the holy grail of info. Here are some of the finer points, but make sure you read the whole article if you are interested in how to best influence your readers to share posts. Also check out these white papers at Sysomos for more detailed information on different social networks.
Twitter is a broadcast network: Look at the following graph made by Sysomos as part of it’s engagement report.
According to Social Twist, Social networks are the most popular way to share followed by email.
Facebook is the most popular way to share via social networks.
No surprise there right?
Twitter is more effective for click-throughs
Again all of this information is from Fast Company’s article, “This is a Click to Action.”
Have you ever clicked that Facebook like button? Then you are a “liker.” Congrats! You typically have 2.4x the amount of friends than that of a typical Facebook user. You click on 5.3x more links to external sites than the typical Facebook user.