It was the year of the check-in and Facebook wasn't about to let FourSquare get a free pass. Facebook introduced its Places service in August to let users share their every move. Using GPS and cell towers, Places lets users to "check in" on their mobile phones to the restaurant, bar or museum they're at, alerting their friends to their whereabouts. While the company hopes the service will allow them to tap into more small-business advertising, users are just glad they now have one more way to stalk their exes.