Syndication and Metadata
RSS is probably the best known metadata format around. RDF is probably one of the least understood. In this essay, published on my O'Reilly Network weblog, I argue that the next generation of RSS should be based on RDF.
RDF can be seen as the HTML for data on the Web -- it's a pot where you can throw a bunch of data and computers can then do useful things with it. In the same way HTML is a freeform mode of expression for content, which humans can then do useful things with.
Like some W3C specs, though, RDF is rather difficult to understand and surrounded by a lot of academic talk and complicated discussion. The Web would be a much richer place if just some basic uses of RDF escaped. RSS would be a great starting point.