Ontologies have been used for quite a while in enterprises for things like information integration (EII). It also depends of how strict your definition of ontol

Ontologies have been used for quite a while in enterprises for things like information integration (EII). It also depends of how strict your definition of ontology is. If you ask me, RSS standard is the most widely used ontology on the web. IMO, the reason why FOAF, DC and similar standards never took off is beacause, unlike for RSS, there were never really any "killer" applications that utilized them.