Facebook introduced an often-rumored check in feature last night with it's new "Places" service. The service is similar to other offerings like Foursquare, allowing you to check in at different places. What makes Places different is that you can tag friends that are with you (definitely want to make sure your friends don't tag you when you're playing hooky from work). Also, after you check in at a destination, you can check and see your friends who have checked in at the same place.
