The Resource Description Framework is a good idea. In practice, however, it's fairly broken, in that it cannot be validated. Given that, for every application that I can think of, people are better expressing their metadata in XML (which is, of course, a meta-language) which allows the information to be less verbose and, if they want, valid XML. RDF and RDF Schemas are essentially XML and XML Schemas wrapped in one level of markup.
IMO, of course.