Well, I recently had a need to write-up an OWL ontology describing the components of a 4Suite repository configuration file (which is expressed as an RDF graph, hence the use of OWL to formalize the format). There has been some mention (with regards to the long-term roadmap of the 4Suite repository component) of the possiblity of moving to a pure XML format.
Anyways, below is a diagram of the model produced by Semantic Works. I still think Protege and SWOOP provide much more bang for your buck (when you consider that they are free and Semantic Works isn't) and produce much more concise OWL/RDFS XML. But the ability to produce diagrams of this quality of a complex OWL ontology is definately a plus.