A study from BrightEdge examining the prevalence of social plugins on the home pages of major sites shows that Facebook is still the most dominant social button on the web. Google +1, however, is growing quickly, having seen a 28 percent increase in adoption over the last month.
Since figures were tallied in June, Google +1 has risen from 3.5 percent adoption to 4.5 percent, a 28 percent increase. In terms of button presence on the home page of the top 10k sites measured, Google +1 has already surpassed the Twitter tweet button plugin in web popularity
http://searchenginewatch.com/article/2092682/Google-1-Button-on-More-Homepages-than-Tweet-Button