According to estimates posted this afternoon, Google+ has really benefited from opening its doors to the public.
Ancestry.com founder Paul Allen fancies himself an "unofficial Google+ statistician." He says so right on his Google+ profile. He oftentimes posts users statistics for the new social network, and today he is claiming that Google+ has hit the 50 million users mark. This comes in only 88 days of existence.
Allen's methodology involves using U.S. census data to track certain rare surnames across Google+. He uses that data and extrapolates it across the world to produce an estimation on total user population. Previously, Allen said when Google+ would be hitting the 10 million and 20 million marks, and was pretty much correct.
Now he's saying that Google+ has over 50 million users, and more importantly, it has grown significantly in the last little bit. Since Google opened the doors and allowed users to join Google+ without an invite, users have flocked to the service at a rate of 4% a day, or a 2 million user increase. In the first 2 days of opening up to everyone, membership jumped 30%.
Here's a graph showing how fast the growth has been compared to other prominent social sites-
All I know it that If I was Google, I would be pretty happy with that rate of growth since going public.