While the initial UDDI specification focused on Web service description and discovery on an Internet scale, subsequent UDDI refinements brought the registry standard increasing into the realm of more traditional enterprise computing as well. Version 3.0's most significant improvements allow an enterprise to introduce Web services gradually: Starting from internal pilot projects, UDDI 3.0 facilitates gradual migration of a service to a shared, intranet-style setting, then to the enterprise extranet, and finally to the Web. In that way, Version 3.0 expands UDDI's initial mission. (...)

The UDDI Version 3.0 specification addresses the complexity of registry topology, and defines how registries may form a federation. A key aspect of such federations is the mechanism by which a registry entity may be promoted from one registry to another, and how global registry key uniqueness is maintained. (...)

The ability to federate registries augment UDDI's original mission, and brings the registry standard within the common enterprise IT environment. Currently, naming and directory services are increasingly the standard way enterprises publish and share information about common technical infrastructure. Therefore, it may seem desirable to register newly created Web services in the enterprise naming and directory service as well. Because a UDDI registry is specifically designed for Web services, it offers benefits that naming and directory services do not normally deliver.

Read What's New in UDDI 3.0 - Part 1

Does anyone use UDDI out there?
What do you think of UDDI, in general?