Foursquare Day is a celebration of the mobile app Foursquare which will record where you are, list suggestions of things to do and eat, and let you know if any of your friends are there too. It also has a game aspect in that you can earn badges by visiting different locales.
Various businesses have used it as a promotion. In 2010, McDonald’s gave customers checked into their restaurants on Foursquare Day a chance to win $5 and $10 gift cards. A 33% increase in foot traffic to McDonald’s venues was reported.
Letting the world know where you are has its drawbacks as well. In 2010 Please Rob Me was launched which used data from Foursquare and Twitter to list people who weren’t at home.