While the subject might sound dark and scary the reality is the Solar Frameworks config system is one of the things that I truly enjoy about Solar 99% of the time. Its that other 1% you need to be aware of to keep yourself out of the rabbit hole.
The notes that, which the configuration file can start out simple (and easy to access inside you application), strange things can happen when you try to access unset values or properties. Defaults can be used and confusion can happen. He also touches on database configuration confusions and how it can all work with your environments (development/qa/production).