SOA is about a triangular relationship - producer, consumer and directory. It seems simple. The UDDI represents the directory leg of the relationship, and in my opinion (and I'm not alone) has been a failure. When most people see UDDI for the first time, they usually ask questions like, "couldn't I just stick this information in a database or in LDAP??"
I recently had a discussion with an architect at a leading online brokerage house. He commented that they had looked at UDDI but thought it was overly complicated while simultaneously delivering a lack of functionality. Wow. Useless and a pain in the ass - that is hard to do. Well, these guys punted on UDDI and spent a day writing a small directory using RESTish terms with easy http access. They are very happy.
I'd like to highlight some alternatives to UDDI - if anyone wants to shoot me a note telling me how you're solving the problem or other alternatives, I'd love to hear from you.