I'm sure you've heard about Foursquare, a game and geolocation app that lets people "check in" to their favorite spots virtually when they're walking in physically. Well, Facebook now has a geolocation app like that called "Places," so users can use their cellphones to let their FB friends know where they are (only in the US at this point). In addition to checking in, FB users can "see who else … [Read more...] about Facebook adds ‘Places’: Cellphone location service