Misused is key... The idea of a self-describing data set is pretty cool, and could have a good use if you had to dump a data-set to be consumed by some external 3rd party without any other documentation... (when has that ever happened)
What maddens me is when people use XML to communicate with themselves. It is the biggest waste of bandwidth and processing power, when there are much simpler formats.
Many years ago I took the XAjax library for PHP and re-wrote it without XML.. Using 2 simple delimiters instead, the code was 80% smaller.
My first thought when I read that was, "I can't remember the last time I heard someone rate it positively." I would probably have to go back to the days when everyone expected a transition to XHTML, which would end the tyranny of broken HTML markup on the Internet. Perhaps in those days, it had some positive ratings.
I don't think XML is overrated but certainly overused and misused.