Foursquare now has more than 3 million users, if the site's public user registration numbers are correct.
The 3 millionth member appears to be Brian S. from St. Louis, Missouri, who has yet to check in to any venues via the mobile-based social network.
Foursquare's growth has been accelerating rapidly lately. The service hit 2.6 million users on August 2, up from 725,000 in March. The launch of Facebook Places, which many thought would bring about the startup's demise, instead resulted in the biggest day of signups ever, CEO Dennis Crowley recently revealed.
Given that Foursquare appears to have a little more than 3.02 million users now, we can determine that it is growing by more than 15,500 users per day (a little less than the 18,000 per day Crowley told the LA Times last week), or nearly half a million users per month.
Although already rapid, that rate may very well pick up now that Foursquare has taken over Times Square.
Update: The team at Foursquare has informed us that they have not, in fact, reached 3 million users yet, but expect to hit that number either today or tomorrow.