Safesquid (http://www.safesquid.com), formerly Middleman when it was opensource, uses TinyXML extensively with great results. It is used for the configuration file, section file (definition of available configuration options with inline help used to construct classes), and to parse results from the F-Prot scanning daemon when checking a file for viruses.

One of the more creative uses I've done with it is used it to synchronize configuration between proxies in a cluster. The proxy wishing to synchronize will request the XML file through HTTP from the master, and the master will dynamically generate it using TinyXML, then the slave proxy parses and reloads configuration sections with it. TinyXML made that all possible with only about a half hour of coding.

TinyXML was the only good XML library I could find which had a license that allowed it to be integrated into the code, rather than placing a burden on the end user to install yet another library.

I should get a job in marketing :)