Most critics believe Google+ is gaining popularity online, but at least one study figures Google's latest social experiment is growing at rates that rival Facebook's. The search giant's two-week-old social network, currently in a limited field test, reportedly grew by 350 percent between July 4 and July 10 from 1.7 million users to 7.3 million. Google+ is also set to hit 10 million by Tuesday and 20 million by the weekend, according to one study.

Those growth numbers assume that Google won't restrict users from inviting their friends this week, as Google did the week prior.

The Google+ population estimate comes from Paul Allen, founder of Ancestry.com, who posted his findings on (where else?) Google+. Allen based his work by counting surnames on Google+ and then comparing that count to Census Bureau data.

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