No one doubted when Google+ was opened to the masses last week -- after a short run as an invitation-only service -- that many more users would flock to the new social networking platform.
But I'm not sure anyone expected this.
According to new data from Experian Hitwise, there were nearly 15 million U.S. visits to Google+ in the week ended Sept. 24, up from 1.1 million a week earlier. That's an increase of 1,269 percent!
Keep in mind that the week measured by Hitwise began on Sept. 17. Google+ didn't go public until Sept. 20, so unless many of these visits were casual drive-bys, the numbers should be even higher this week.
Does this mean that Google+ has increased its 25 million active monthly users 13-fold to 325 million? I don't think there's enough data yet to draw that conclusion. Part of the increased traffic undoubtedly was due to the search giant increasing the number of Google+ features to 100 in conjunction with the social networking platform's public debut.
In other words, users who already had accounts may have been visiting more frequently than usual to check out new features such as Hangouts, which allows group video chat, something Facebook doesn't yet offer.
Still, that probably only accounts for a small percentage of last week's huge increase in traffic.
And consider this: The new data does not include mobile traffic or traffic from the Google Notification Bar, according to Hitwise. So last week's Hitwise data no doubt under-counted visits to Google+.
Further, Google's 1 billion monthly users will be reminded of Google+ every time they visit the search site and see the "+You" at the top left of the menu bar. Many of them likely haven't even noticed it yet, but they will.
With 750 million members, Facebook is still far and away the top social networking site on the Internet. Last week, when Google+ soared to 15 million visits, Facebook had 1.76 billion, or 64.85 percent of all U.S. social networking and forums visits tracked by Hitwise.
Also, there's no reason to believe users will abandon Facebook en masse to join Google+. Instead, many will maintain both accounts.
The real question is where they'll spend most of their time. It'll be fascinating to see what the numbers are in three months.