Whilst I don't doubt there are scenarios where developing and rigidly applying a detailed taxonomy structure against your content is a sensible approach that delivers lots of valuable benefits for your organisation... I haven't seen many successful implementations. I have seen plenty of failed attempts. The most common cause of failure is creating an overly complex taxonomy that becomes impossible to implement easily and/or consistently and/or results in making content harder to find (when the opposite is usually desired).
Taxonomy fails when the design does not reflect the use. Richardson looks at the issue that taxonomies are often designed by subject matter experts, while the people using them are not. Unless the SME's impart a lot of their knowledge about the subject to the users, the users are going to use different terms in their attempts to find and categorize content. Frustration ensues.
Taxonomy fails because it's too easy to get too complex (and rigid) with a taxonomy. And the supporting technology (search) places too much emphasis on creating specific metadata in your information management system. I hadn't heard this second argument, though I have experienced it in various settings. Either the search tools completely ignored the fact of how something was tagged with metadata. Or that metadata swamped out all other results. Richardson uses a nice example to walk through how it happens. That said, this seems like something that should be manageable with the search algorithms that are available today.
As a final note, taxonomies (and metadata) are not evil. Many people and organizations find them very helpful. The concern is that there has to be a balance with the people and the technologies, so that work can get done in the organization.