Dan Zambonini at XML.com - The 7 (f)laws of the Semantic Web:
"Creating metadata and classifications is difficult (let’s not get started on Ontologies). People are biased (whether they mean to be or not), and fallible. Metadata, which the Semantic Web relies on, is not always going to be of great quality.
[...] My clients don’t want to create ontologies. They don’t want to map one set of data to another. They want to use something that’s out there and ready for them to use, and will give them the maximum benefit (so if the Imperial War Museum say that they have a tank from “World War One” and the Science Museum has a video of the firing mechanism from a gun from “World War One”, they can both use the same term/URI)."