There are thousands of Plone powered websites all around the world. They are used as CMS, Intranets, social networks, and others. I can imagine that every country has at least one Plone site and there is a Plone content in every major language. I myself contribute to few Polish, Dutch, English and Swiss sites.
List of major Plone websites that have more than 1 line of Python code I’ve written. Some of them I created, some only maintained or helped developing.