Google SVP of social, Vic Gundotra, apologized for the spamming on Saturday.
"For about 80 minutes we ran out of disk space on the service that keeps track of notifications," he wrote in a Google+ post. "Hence our system continued to try sending notifications. Over, and over again. Yikes. We didn't expect to hit these high thresholds so quickly, but we should have."
Buried in Gundotra's apology is acknowledgement that Google+ is growing quickly. Though the service is only offered as a "Field Test" at the moment, Google is now letting early adopters invite friends at will. Initially, invitations were available in limited numbers.
Google declined to comment on the number of users in its Google+ field trial.
But Paul Allen, founder of Ancestry.com, offered his own estimate: 4.5 million. Allen's method relies on counting surnames present in Google+ and dividing that number by the number of people in the U.S. said to have that surname, based on U.S. Census Bureau statistics, in order to project a total number of users. Other self-appointed statisticians have suggested that the figure is more like 6.4 million and that the user base is growing by about 500,000 daily.
Facebook, with more than 750 million users, still has a commanding lead and probably will for years. And Google+ is likely to see its growth slow after early adopter fever subsides. But at the very least, the early enthusiasm for Google+ means that Google+ won't follow the trajectories of Google Buzz or Google Wave, which failed to gain traction with users. It may also mean that among early adopters at least, there's hunger for a competitor to Facebook.
Google's plans for Google+ can be seen in its solicitations: The company is asking Google+ users how they'd like Google+ to interact with Gmail and with Google Docs. It's planning a pilot test for business Profiles, to understand how Google+ users interact with brands, and it's planning to provide developers with APIs for creating applications that work with Google+.
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