I wish there existed a popular config format that was somewhere between YAML and JSON. In my current nodejs project I sometimes use js files for config because js supports comments and is more lenient on syntax then JSON. I prefer using { } to group objects, rather then YAML indenting, but otherwise am okay with YAML and only don't use it because the parser is not part of Javascript or nodejs.

Yaml is not good for configuration files because it is not easily human-editable. It seems "easy" but meaningful whitespace is a cluster-fck.

Edit: I have been looking for reasonable configuration file formats for a while. Json actually has pretty bad human-readability at any scale because of its quoted key-values. Yaml is easily readable but when a user tries to change anything, things go to hell. The humble ini-file has won so far. It's limited and not fully standardized but it is human readable and human writable. I'd love see something better but human readability/writable is going trump all sorts of cleverness.

Edit2: From http://en.wikipedia.org/wiki/YAML "The specific number of spaces in the indentation is unimportant as long as parallel elements have the same left justification and the hierarchically nested elements are indented further."

Yeah, a user of your software is going to be able to understand when they mess up on that rule, riiiight. Screw Yaml.