Are corporate taxonomies obsolete?

A client was recently asking me to discuss the merit of having a corporate taxonomy when recent trends seem to be favoring folksonomy or tagging. As a reminder, a corporate taxonomy is a categorization system that all staff must use to classify documents they file online; wheras a folksonomy is an ad-hoc categorization system where staff choose their own words to classify their documents. I strongly believe that although the concept of letting people tag their content is wonderful for the Web as a whole, it is important for corporation to agree on what words to use to categorize their own documents. In other words, a folksonomy only really works when you have many, many people creating and classifying content. Corporation have their own, often precise vocabulary that staff must adhere to otherwise it would be very difficult to find documents.