UPDATE: locamatic is not maintained anymore as far as I can tell. Check out my post on a replacement: ControlPlane
Glad I found Locamatic, because I need to set different network location profiles on my Mac based on where I am in order for the network to function properly. It works by checking which wifi or ethernet connection is active, and setting the location based on which network you associate with that location. It installs as a pref pane and lets you add, change or delete the location to network entries, as well as select a default printer to use while on a particular network.