Robert Siciliano, CEO of IDTheftSecurity, noted recently on the McAfee blog that apps like, "Foursquare, Facebook and Yelp allow you to check in' at places using your mobile phone, and then share your location with friends or on social networks...It can actually be a nifty tool...like when you are trying to find directions to a place: the map begins your directions where you are, since it knows your location. Some businesses even provide discounts or freebies as a reward for checking in."
http://news.idg.no/cw/art.cfm?id=01EC3B8E-A663-57E0-733137795C3817A4