I've spent today writing on an essay on the Semantic Web, and reading up more particularly on OWL.
What hits me is the complexity. The OWL Guide was a big help, but I still find it difficult to see how to apply it to the real world. I mean, I can see the potential - the idea of being able to effectively convey semantics, even in the the face of data using different ontologies, and the promise of being able to query about properties that are not explicitly written out in the data through machine reasoning.
But I've yet to find a tutorial or introduction that explicitly address more directly useful scenarios instead of the "let's build a complex ontology" scenario.
That, and the lack of a wide choice of tools to reason about OWL ontologies means that we're likely still years away from seeing the real promise of the Semantic Web realised.
In the meantime there is still lots we can do to approach the Semantic Web gradually. One of the main things is to embrace RDF directly or through RDF-A or GRDDL. Without OWL we're stuck doing things like inferring mappings between various ontologies by ourselves, but the more widespread RDF datasources become, the more incentive are we creating to invest in creating tools that can solve the interoperability issue (whether by making OWL usable, or by finding something else).
I'm curious about to what extent the complexity of OWL is needed, or whether it is complex because the problem is still not sufficiently well understood and a simpler solution may come along.