My first graduate job at a large British telco involved a lot of XML...

- WSDL files that were used to describe Enterprise services on a bus. These were then stored and shared in the most convoluted way in a Sharepoint page <shudders>

- XSD definitions of our custom XML responses to be validated <grimace>

- XSLTs to allow us to manipulate and display XML from other services, just so it would display properly on Oracle Siebel CRM <heavy sweats>