Clay Shirky does a great job explaining why the Semantic Web is a myth:

"Descriptions of the Semantic Web exhibit an inversion of trivial and hard issues because the core goal does as well. The Semantic Web takes for granted that many important aspects of the world can be specified in an unambiguous and universally agreed-on fashion, then spends a great deal of time talking about the ideal XML formats for those descriptions. This puts the stress on the wrong part of the problem -- if the world were easy to describe, you could do it in Sanskrit."