If you're an iBook/PowerBook user who is constantly fiddling with various settings depending on where you are, point your mouse towards Location X for the solution to all your preference-changing woes. I only played with this for about 5 minutes before plunking down my $20 for it, as I am already in love. This app makes me cry out "why doesn't OS X do this already??" Then I realize I'm alone in my apartment right now, which just makes me feel weird.
Anyway, Location X is essentially a management app for all the various settings you might have to constantly set and reset, depending on which networks your Mac connects to throughout the day. For example: in between classes, I use wifi at Starbucks since all of the networks on my campus have most of their ports restricted. Well, Starbucks' wifi treats SMTP servers that require authentication in an odd way, so I'm constantly having to change my SMTP server when I sit down for a cup o' joe. But Location X, as you can see in my screenshot, can do so much more. Not only can this latest v2.5 do automatic network detection, it can set default printers, adjust energy settings, change browser homepages, run applescripts, change security preferences and so much more. It even has a plugin architecture, opening the doors for anyone else to build in even more settings and functionality.
I highly recommend this app for any of you mobile warriors out there who are tired of constantly adjusting settings like these, simply because you're on the go during the day. Location X is shareware which costs $20 (a bargain, if you ask me), while a demo that allows for 8 location switches is available here.