If you've ever seen the web.config file that ASP.NET uses, and thought, "Wow, I'm so glad they configure things that way, in this nice, easy-to-use XML file. Wish I could do that!" then you should check out the System.Configuration namespace. There's an interface called IConfigurationSectionHandler that lets you write your own parsers for your application configuration file, letting you put whatever you want in there.
I've written a bunch of these over the last few months, but today I wrote the last one I ever will.