Facebook has just announced a new security feature to users that allows an account to log themselves out from a remote device. Users will find this in the Account Security section of the account settings. There will be a menu showing "Most Recently Active" and "Also Active". Also Active will only be displayed if your account is logged into multiple locations.
From this interface, you will see the login time, browser, location based on IP address, and operating system. Any of the sessions listed there can be ended with a single click. This might be of use in case you accidentally leave yourself logged into a friends computer, or (for some reason) a public computer.
This feature isn't available for everyone just yet. Remote logout is being rolled out slowly to Facebook's massive user base. Have you ever accidentally left yourself logged in to another computer?