Greetings,
I am currently using XML to configure a parser object I have created for aggregation and scoring of behavioral data generated from psychological research studies. These studies record experimental sessions that are later "coded" by research assistants using a 3rd party behavior coding program. The "codes" they generate corespond to behavioral actions or experimental models. The experimenter presents a given model and the subject is scored on how well they imitate or how frequently the do some action. I take the configuration files from the 3rd party software and parse it into an XML structure (using HTML::Template for configuration file generation). Once the XML is written I then tweak it to fit the needs of each specific study. I load the resulting XML into my parser object with XML::Simple to get it into a Perl data structure that I can use for parsing of the generated "code" files. It makes the entire process much easier than hard-coding the data structure since the research leads can add and subtract any given element in the XML configuration files as they see fit. Once the data is parsed and scored the statistical analysis can begin. It has saved many a man hour since the scoring and such no longer needs to be done by hand.
In the past I have used XML with SQL, Perl and Flash ActionScript to get dynamic content into Flash presentations for online portfolios and configurable, clickable city maps. With the widening suppor for XML in different programs, sharing data between software packages has become more and more of a reality.
I initially scoffed at the idea of XML since most of the buzz surrounding it was how it would revolutionize document searches and such... stuff that good design and a reasonable database should accomplish. However I have since "seen the light" and now use XML to describe the structure of my data in a configurable way.

-InjunJoel