From Sebastian Sparrer:
AFPStatus gives you a very simple icon inside your menu bar that will show you the current status of your file sharing with one look. It will show you if file sharing is enabeled or not and it will list the IP-Addresses of other users currently connected to your Mac. And with a klick on the address it will be copied to your clipboard.
Additionally, there is the possibillity to turn file sharing on or off and to access the "Sharing" preference pane through the AFPStatus menu. And, with GROWL installed on your system, you can get additional notifications.