XML for configs is fine, as long as you treat it as a binary format. Which means having tools to help manage those configs. Too many people use XML for configs and then call it done, which makes for a terrible experience.

XML with config helpers and the ability to open it in an editor and see what is going on and tweak it is a great experience. XML with the expectation that an editor will be used to configure it is a terrible experience.

The above also applies if you replace "XML" with "JSON". :-)