Yeah, the OS X preference for config files and other things is .plist files, aka XML. By what I understand, they have an API that makes it real easy for a program to save settings to ~/Library, similar to the API hools in Windows to save to the registry.

The use of XML by both Trillian and Proteus made it pretty simple to migrate my massive IM list over, keeping my custom renamed contacts and metacontacts in the move.