There was a time where both Google Chat (whatever it was called back then I lost track) and Facebook Chat were built on it. So you might have.
Google Talk - and it was an actual federating XMPP server, in contrast to Facebook which merely allowed you to login with an XMPP client.
You're right. I know at least one company used XMPP for things like customer support chat too. So maybe I have. I just mean the last time I used it intentionally was a long time ago before I was worn down futilely trying to convince friends to use it instead of locked down chat apps.