Unofficial Google+ statistician Paul Allen (Ancestry.com founder) has been projecting Google+ user stats since day one. And his big news on Wednesday is that Google+ has busted through the 100 million user barrier.

This comes just under two weeks after Larry Page announced that the network had reached 90 million users. Page said that 60% of those users engage daily and 80% of them engage weekly. So according to him, we’re not talking about a majority of dead profiles here.

According to Paul Allen’s estimates, Google+ has grown more the 10% in 13 days. This bodes well for future growth, as he predicts that by the end of 2012, Google+ will be a monster:

Meanwhile, I think it’s noteworthy that Google+ membership has grown more than 10% since Jan. 19th when Larry Page announced 90 million users. I have them at 100.8 million users by the end of the day. They have been growing by more than 750,000 new users per day since the 19th, based on analysis of users with hundreds of different surnames. If that rate holds steady, Google+ will end the year with 345 million users. But as I have said before, Google has many dials and levers to use this year to increase signups and usage, including its Android 4.0 rollout. I stand by my prediction of at least 400 million users by the end of 2012.

You can check out his full rundown of why he thinks Google+ will hit 400 million users here. Allen’s methodology for estimating user data involves tracking surname popularity among U.S. Census Bureau data and comparing it with Google+. He then extrapolates a sample out to non-U.S. users. More on that here.

If anything, his previous estimates have been conservative. Before Larry Page’s announcement, he predicted that Google+ would hit 85 million users by February 1st.

These totals are indeed impressive. It probably helps that as of now, a Google account sign-up means a Google+ sign-up automatically.

Apparently, Google+ is more than just the thing that prompts Gmail users to ask “What the f*ck is that up there?” (See below)

Are you seeing more people you know on Google+? If so, are they engaged in the service? Let us know in the comments.