XML, and surrounding technologies like XPath, XSLT, Schematron, RelaxNG, etc. by extension, are extremely useful as data storage and validation languages. If I was planning to keep structured data around for a long time on disk, and want to make sure that I didn't have garbage stored, I'd definitely want it in XML, with a fairly strict schema to validate that data.

If you're writing an API that works with files (not an over the wire format), and you don't want to be locked into any one language or toolset, XML is pretty hard to beat. Being able to write just one XSLT file, and have it processed by any compliant processor is pretty impressive - no other templateing format works that way.

The problem for most people is that they never touch those other technologies that make XML great, because they're looking at basic data serialization, and don't care so much about validation and transform. Most web technologies fall into this category. Any tool can and will be abused - how many of us have seen a monstrous unmaintainable Excel file that performs a task that would be much better done in a scripting language?

TL;DR: XML tech has it's uses, but it's very frequently abused.