BOOM.
There are charts and stories like this going all over the Internet. However you should not draw a conclusion from this as it is not a apples to apples comparison.
Facebook was a new company that limited its users by colleges for the first few years. Twitter was also a new company. Google+ while a new feature is leveraging 100’s of millions of current Google users in various products. As a example I don’t think Facebook or twitter was able to put there badge next to almost every search result made like Google did with +1.
And as a second note in social hyper growth does not always convert to engaged users, that is the real stat you want to watch to understand google+’s success.
