16 is squaring four therefore April 16th now Foursquare Day. Foursquare users built loved the idea of dedicating a day to the online check-in service.  Foursquare’s founders loved the idea too.  New York City Mayor Bloomberg has given the idea the NYC seal of approval. He even delivered a Mayoral Proclamation at the Foursquare offices. There are other cities that are also doing events as well if you take a look around the web.