Mac: We've discussed ways to ways to make your computer adapt to your environment, but if you'd rather make your Mac do it all for you, Sidekick is a utility that will adjust your network settings, change default printers, start or close apps, and more -- all based on your physical location.
Sidekick is made for people who travel, or at least anyone tired of manually switching default printers, network settings, disconnecting or connecting to servers on the network, and more every time they get to the office or go home for the night. Once installed, tell Sidekick where "home" is, where "work" is, and any other locations where you'd like the application to adjust your settings. The app then uses Mac OS's built-in CoreLocation positioning service to get your position when you arrive, and while it's not super-accurate, it's enough to tell whether you're at home or at work and adjust your system to match.
The app can tweak common system settings like your network configuration, turn Wi-Fi on or off, change the default printer, and open or close installed applications, but it can do much more as well. The app allows you to select "actions" to perform when you arrive at a specified location, like changing your Adium or iChat status to reflect that you've arrived at work, change the screensaver settings to require a password, automatically connect to a network location, and even change your wallpaper to suit the location.
Sidekick used to be known as an app called Network Location, but the developers have given it a new name and an overhaul for it's recent release. It'll set you back $US29, but if you travel often it may be worth it.