Clay Shirky talks about the Semantic Web in a piece he calls The Semantic Web, Syllogism, and Worldview. In an effort to explain what the semantic Web is all about, he sums it up better than anything else I read:

The simple answer is this: The Semantic Web is a machine for creating syllogisms. A syllogism is a form of logic, first described by Aristotle, where “…certain things being stated, something other than what is stated follows of necessity from their being so.” … This is the promise of the Semantic Web — it will improve all the areas of your life where you currently use syllogisms. Which is to say, almost nowhere.

I have nothing else to add.

Link