Do you use location based service Foursquare and encourage your fans to? Have you made it part of your marketing plan yet? If not, you may want to. Over the weekend Foursquare - a mobile serivce where members note their locations, can find out where friends are and earn points and badges - hit 10 million users just 15 months after launching. Foursquare posted a great infographic celebrate the announcement on their blog.