Today is the third annual 4sqDay. They chose 4/16 because 42 = 16. Foursquare announced a major milestone today to celebrate 4sqDay. They have hit 2 billion check-ins and now have 20 million users. Anyone that checks in today will receive the 2012 4sqDay badge and will receive this message:
In 2010, foursquare fans declared April 16 4sqDay (4/4^2 ? nerds after our own heart!). Two years and two billion check-ins later, you?re still why we get out of bed each day. Thanks to all 20 million of you for making us part of your lives. Happy 4sqDay!
Foursquare hit 15 million users back in December. The company has raised over $71 million in total funding and is valued at $600 million.