Worth reading: Dan Zambonini at O'Reilly's XML.com provides some constructive criticism of the elusive Semantic Web, outlining seven flaws. Zambonini calls himself a "disillusioned advocate" of the Semantic Web.
1. Not all Semantic Web data are created equal.
2. A technology is only as good as developers think it is.
3. Complex Systems must be built from successively simpler systems.
4. A new solution should stop an obvious pain.
5. People aren’t perfect.
6. You don’t need an Ontology of Everything. But it would help.
7. Philanthropy isn’t commercially viable.