I'm not a great fan of metadata in the context of HTML, I really am not! When it is mentioned I get all sorts of visions of seedy little SEO guys playing with the placement of words in the head of HTML pages and getting excited by a 0.0001% increase in PageRank... makes my blood run cold and makes me feel not just a little poorly that does. Metadata on the whole is okay mind, information about information is how the Semantic Web will come about, but for the sake of SEO it's just not cool and puts me in mind of Witch Doctors demanding sacrifice to ensure a fruitful harvest.
So metadata doesn't have to be evil. Just like some Evangelical Christian like Harry Potter books/films, some metadata is a cool thing and will help intelligent agents of the future parse data and produce relevant information.
The DCMI is an independent body which is seeking to standardize metadata and seems, at its heart, to be academic in focus rather than business orientated so - while I appreciate that some people use their websites to generate sales - while a purely business orientated way of adding metadata things leads me back to thinking of those scruffy, sweaty, slightly shambolic buggers crouched over their keyboards and frantically checking their PageRank after each tiny, little, minuscule iteration... using the DCMI's Dublin Core allows my academic leanings to embrace it and, hopefully, improve PageRank as well.