I probably use Semantic X more than most people do and I absolutely never understood RDF/OWL/whatever. My use case: I run a fairly large wiki, we have Semantic MediaWiki installed, and literally the only thing we use it for is setting "facts" on pages that you can use as a search engine to find the pages that satisfy queries. It's just metadata for pages, essentially.

I don't think I'm alone in this. None of Semantic Web stuff ever really made sense to me.