XMPP Case Studies
This page gathers link to various use cases of the XMPP protocol. Some of them are published by software vendors. They might be biased but give a good overview of what could be done with the XMPP protocol. It is up to the reader to keep its critisizing ability :)
XMPP and VoIP
XMPP for Government
XMPP for Enterprise
This section cover cases of internal use of XMPP servers.