When would XML be appropriate to use? Should it ever be used in conjunction with MySQL? What kinds of applications are people writing that are taking advantage of these two technologies, either by themselves or together?
Right now think XML is most useful for providing a data inferface between systems.
Here at work for example, it's a very mixed environment - Solaris, Linux, AIX, Windows, and even a mainframe all running server applications. We're using XML more and more to pass data between them.
Also getting some of the system to make system status info available by connecting to a port and receiving a "dump" of XML data. This then gets parsed by PHP on a webserver so we can look at what's happening to a particular server.