XML, despite still having immense momentum, is not without problems. These days it probably is the pragmatic solution for many jobs, thanks to the multitude of tools for various platforms for processing it. That doesn't mean it couldn't, and shouldn't, be better. Not surprisingly, people persist in discussing its faults and how it should be.
Erik Naggum, in his characteristic style, details his beef with XML with a very long article [via Python Owns Us] where he makes many good points about the evolution of data formats and gives his suggestions on what should be changed in the XML format to make it better. While I'm not totally convinced about the binary format bit, otherwise I do agree with his points.
However, I think Aaron Swartz put it best in one little sentence, even if he didn't suggest any improvements: "XML [...] encourages you to be conservative in what you accept and liberal in what you put out.", in direct contrast to the traditional — and sensible — ethos of protocol designers. That is the single thing that is most damning to XML. Thanks to Aaron for articulating it.