NBML - Not Bunk Markup Language and Musing about Markup - Here are two excellent posts about the tension between data parsability and data editability. XML is wonderful for the former, tolerable for the latter. I tend to use a modified INI format for configuration files, since it’s total cake to edit and fairly easy to parse. That you can’t keep nesting items within items is a plus, since it forces you to keep your configuration easy to understand.
One question about NBML: isn't the use of tabs in makefiles one of the reasons people hate them so much?