As you may know, UDDI (Universal Description, Discovery and Integration) was originally designed for publicly accessible registries. As part of making this possible, UDDI includes an "elegant" (engineer speak for "indescribably complex") mechanism for defining taxonomies (known as tModel's for those that have had the pleasure of working with them). It was once thought that taxonomies and categories are supposed to make it easier to find relevant information when you wanted to search for web services.
Then a funny thing happened. First there was Google. No need to scan through a hierarchy of terms to find the relevant terms (which you would have probably organized differently and certainly interpreted differently than the original authors intended) -- you just type in a few terms and voila, you have reasonably relevant matches. People suddenly realized that taxonomies aren't necessary, and in many cases, got in the way. The 1-2 punch came from tagging, comments, ratings, and other "folksonomy" related tools which have all but assured the death of taxonomy based approaches.
SOA What? With all of this Web 2.0 development, it's clear that internet scale folksonomies work far better than taxonomies. On the other hand enterprises are, for the most part, stuck with UDDI-related SOA governance tools and their strict taxonomy and categorization mechanisms. The open question though... is this really a problem?