My main concerns with XML are that it gets very verbose as  you add more options and things like commenting are hard / ugly.  I tried to write the same hadoop example is YAML (https://gist.github.com/shivaram/5123598) and JSON. https://gist.github.com/shivaram/5123599 

The YAML one looks more nicer and also has elegant comments that can be a part of the config. However YAML parsing isn't available in the scala library and we'll need another dependency to parse this.

Another option to consider is the typesafe config library. https://github.com/typesafehub/config . This is Scala friendly and is used for akka configuration --It looks like a modified version of JSON which is easier to write.