The staggeringly fast growth of Google+ has finally slowed down a bit. Last week, when up to 2 million people a day were joining the site, Ancestry.com founder Paul Allen used his surname model to estimate that Google+ could reach 20 million members by this past Sunday. But the mad dash to join the social network has died down, and by Monday, when a mere 750,000 members were added, Allen estimated the site’s user base at just under 18 million.
As the site’s membership numbers surge, Google is adding new features to make the most of its popularity. As of today, Google+ users can now upload address books from Mac, Outlook, and other sources to find and invite new friends. TechCrunch has posted uploading instructions on its site.
Google also finally released an official iPhone app for Google+ yesterday. Previously, the only app available was for Android phones. Within just 24 hours of the iPhone app’s release, Google+ became the most popular free download in Apple’s app store. According to TechCrunch, the app started out buggy and is still buggy after the “fastest update to an iPhone app” ever, but Google+ users desperate to access the site through an official app don’t seem to care too much.
Despite Google+ boasting 18 million users, Google doesn’t seem to think that there are quite enough famous people using the social network. So it’s launching a “celebrity acquisition plan” to increase important-person awareness of the site, offering them account verification (something that William Shatner could have used recently) and maybe even a “verified” profile badge à la Twitter. Google is still figuring out how the verification process will work; asking celebrities to fax their drivers licenses to the company or having their talent agents file the requests directly are a couple of options said to be under consideration.