Google (NASDAQ:GOOG) revealed more than a year ago that it has more than 1 billion searches a day and averages 1 billion searchers a week.
Now it can add 1 billion unique visitors per month to that storied stat club. comScore revealed that Google's Websites, including its search engine, YouTube video-sharing site and Gmail, lured more than a billion unique visitors in May. That's up 8.4 percent from a year ago.
That would be nice if it weren't for the fact that Google's rivals are growing their online traffic, too. Microsoft, whose Bing search engine came on strong last year, followed with 905 million unique visitors in May, good for growth of 15 percent.
Facebook, meanwhile, saw its visitor count balloon to 714 million visitors, perhaps an accurate reflection of its current user base. Facebook's year-to-year growth was a remarkable 30 percent.
More impressive (and scary, for Google) is Facebook's user engagement stat: comScore said the social network's users logged 250 billion minutes worldwide in May, up 66 percent from May 2010.
In a June 15 blog post, comScore said Facebook's average U.S. visitor engagement has grown from 4.6 hours to 6.3 hours per month over the past year. Nielsen confirmed the six-hour stat in its own research.
Microsoft is next at 204 billion minutes, down 13.6 percent, while Google is third with 200 billion minutes, good for growth of 13 percent.
Facebook's ability to keep users logged in the walled garden is the reason why Google is logically infusing its Web services with social software.
This Web phenomenon is also the reason Google has been revving up its mobile and display advertising efforts. The company acquired mobile ad maker AdMob for $750 million last year and agreed to buy display ad player Admeld last week.
Google has also accelerated its YouTube efforts, adding thousands of streaming movie titles and using Google TV as a new access point for YouTube and its display ads.
Near-term, Google has little to worry about. EMarketer said Google will take 41 percent of all ad dollars, with Facebook netting 7 percent of U.S. online ad spending this year.
What Google is nervous about is that Facebook is getting more users to stay online with its site longer, which means more users are seeing more display ads on the network.
This generates more ad cash for Facebook and its partners. Moreover, ad partners who would normally go to Google, Microsoft or Yahoo for display ad placement now have Facebook as the optimal choice to spread their message. This is why Google has been boosting social -- adding the +1 button -- and why it's been fortifying its already strong ad arsenal.