Airport Location is a free application that I have written for Snow Leopard. Its main purpose is to determine a laptop's physical location via nearby wifi access points, then apply a previously-saved settings 'snapshot' to affect different settings in different places.
If set to operate automatically, Airport Location will scan for location changes on wake. If the program determines that you are at an unrecognized location, (i.e. an unrecognized set of wifi access points nearby), it will ask you to name that location. Once named, a location is associated with a settings 'snapshot' which can either be unique to a particular location, or grouped with other locations (e.g. 'Class', 'Work', 'Meeting Rooms', 'Coffee Shop', etc.).
For a laptop user, Airport Location lets you specify things such as volume level, iChat status, which apps to open or close, desktop background, default printer, and network-related settings (Bluetooth on/off, Firewall on/off, VPN connection on/off, mounting a shared network volume). For example, in a classroom, you might mute the volume, set iChat to 'in class,' open your class-related apps, change the printer, and disable most networking features.
Location-based settings profiles work best on laptops. However, the program is still exceptionally useful for desktop (or otherwise non-mobile) 10.6 machines.
By creating various task groupings on your desktop machine, like 'Doing Work', 'Normal', 'Designer', 'Developer', 'Watching Movies' it is possible to create snapshots customized for each grouping. As example, when 'Doing Work' you may want to set volume to 25%, open work-related apps, set iChat to offline, mount a Bootcamp partition, etc.
When 'Watching Movies' instead, you'd turn the volume up to 100%, set the screen brightness to a good level (75%), change the iChat status, hide the Dock, and set the Desktop background to all black.
There are instructions at the above URL to display current group (or current location) on the desktop via Geek Tool.
[robg adds: Airport Location is a free program that adds a lot of flexibility to a mobile (or desktop) machine. I haven't tested it myself yet, but thought that many of you may find it useful. (Andrew is also one of our more-prolific hinters, with 20 contributed hints here on the site.)]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2010042707531680