Found Cory Doctorow's great piece on why the Semantic Web will not exist - Metacrap: Putting the torch to seven straw-men of the meta-utopia:

"2. The problems

• 2.1 People lie
• 2.2 People are lazy
• 2.3 People are stupid
• 2.4 Mission: Impossible -- know thyself
• 2.5 Schemas aren't neutral
• 2.6 Metrics influence results
• 2.7 There's more than one way to describe something"