Home Zone - user actions based on Bluetooth or Airport networks
The obvious use here is to set your computer to not require passwords when you're at home (or even better, when your Bluetooth-enabled phone is in proximity to your computer), but lock it up tight otherwise. Of course if you're using the Bluetooth functionality, be aware that Bluetooth ranges can vary widely, and sometimes randomly. If you're relying on Home Zone to lock your computer in the office when you walk away from it, you may be surprised by just how far you have to get away from it before it actually locks. Although it seems to take some time for a Bluetooth connection to register network scanning time is configurable in the application preferences, which is a nice touch.
However you look at it this is some seriously cool functionality. Home Zone is a free Mac download.