Google's social network, Google+ , might be one of the fastest-growing networks ever, having already reached 10 million users according to one estimate. Paul Allen , of Ancestry.com -- not to be confused with Microsoft co-founder Paul Allen -- has developed an interesting methodology to calculate the number of Google+ members. He sampled a number of surnames from the U.S. Census Bureau data and compared it to surnames of Google+ users. By comparing surname popularity in the U.S. with the number of users on Google+ with each surname, he can guesstimate the percentage of the U.S. population that signed up for Google+. Finally, he calculated a ratio of U.S. to non-U.S. users to generate an estimate for the number of Google+ users worldwide. The result? Google+ has approximately 9.5 million users worldwide, with 2.2 million joining in the past 32 to 34 hours, according to Allen's estimates. This is amazing growth even for a giant such as Google: We cannot remember any social network reaching so many members so quickly after its release. Coming from a third party, the data is obviously unofficial (we asked Google for comment on these numbers, but haven't heard from them) and should be taken with a grain of salt. If they're true, though, they indicate that -- after so many stumbles -- Google might finally be conquering the social networking arena.