YAML as a data format for application's configuration

It seems obvious that almost every application has its configuration. We can use a lot of data formats for configuration files, for example YAML or XML, JSON or plain PHP (replace with any language you use) files. Personally I like and prefer to use YAML to other formats and here I just want to describe a little one of Symfony components called YAML. Also It's quite interesting for me which format you use, what pros and cons you see, so don't hesitate to leave a comment with your thoughts.