Google's social networking service Google+ finally opened its doors completely to the public a few days ago with no need for an invite. As one might expect, the users base for Google+ has increased rapidly. A Google+ post from Paul Allen, the co-founder of Ancestry.com and a person who has offered up unofficial user stats for Google+ in the past, said that back on September 9, Google+ had 28.7 million users. Allen added that on September 22, two days after Google+ went public, " ... our model shows 37.8 million users, with most of the growth coming in the last 2 days. By adding a fudge factor ... to account for private user profiles and for non-Roman surnames (both of which are totally overlooked by our surname counting model), my current estimate is 43.4 million users."
Allen has also improved on his model for calculating user numbers in Google+. He states, "My earlier model ... which proved to be very accurate in the first 2-3 weeks, did not address either private profiles or non-Roman alphabet. According to FindPeopleOnPlus.com, there are substantial numbers of users from countries like Indonesia, China, Vietnam, Japan, Thailand, and many other countries, which my surname counting approach does not include. So I have decided to add a 5 (percent) privacy fudge factor and a 10 (percent) non-Roman alphabet fudge factor in my Google+ model. I'll need to develop a way to actually calculate those percentages somehow, rather than just guess on them."
So far Google itself has yet to give any official user numbers for Google+ since it went public earlier this week. It's likely that Google won't reveal those numbers until its next quarterly financial report which should be held sometime in October.