Announced today Facebook will begin to notify you if you are signed in to Facebook somewhere else. They say that you will be able to take actions against the logged on user by kicking them off your account. This service is similar to AIM but goes into much more extensive detail on what information it tells you. For example, when you log in it will notify you that you have been logged in somewhere else and it will also tell you how long the device has been logged in for and will even go as far as to tell you the name of the device and the location.
This feature yet very exciting is still in the works but is expected to come out soon. Making it easy to keep your account safe and secure seems to be increasing in the Facebook world and that is turning out to be a very good thing. Facebook has not announced a launch date for it but it should be out very soon.