A while back we mentioned MarcoPolo, a location manager for the Mac that can change certain system settings based on the particular wireless network or devices you're connected to. Home Zone offers a similar capability allowing you to set up a variety of actions (e.g. changing the default printer, starting/stopping the screen saver, starting iSync, etc.) that are triggered either by changing your Airport network or by bringing Bluetooth phone close to your Mac.
Home Zone is presently in beta and a free download from Jonas Witt.
Update: MarcoPolo also does Bluetooth.