Jeff Tonkel of Infravio recently pointed out the importance of the registry in a service oriented architecture. I'd like to second that thought. While I'm at it, I'll go so far as to state my opinion on who is leading in the space.
For starters, you have to look at BlueTitan. These guys get one real simple fact - you don't implement a registry for the sake of having a registry. Many vendors wrote a registry and encouraged their customers to dump crap in it. Bad idea. BlueTitan took the other approach - they started with the 'ilities' and worked backwards into the metadata that needed to be captured to manage a service network. Their registry is designed to capture only 'usable' metadata (actionable information); don't store anything that can't be used. Also they focused on the needs of enterprise grade service networks, the people with the really hard problems. I'm thrilled to see BlueTitan recognize that services are often just 'bumps on the network', that policies are 'service oriented aspects' and that the metadata and registry are the heart of making it functionally scalable. Most networks grow exponentially for some period of time; BlueTitan makes it possible to manage high growth networks on a linear cost scale.
After BlueTitan, you have to look at Systinet. Although these guys started with a strong UDDI slant, I believe they not only understand the limitations of UDDI, but are well on their way to overcoming the issues. I anticipate that Systinet will also have strong 'developer-side' integration into the registry (think reusable assets).
The registry is quickly turning into the 'metadata warehouse' - it is the point where a 'metadata driven architecture' and the 'service oriented architecture' merge. Architects are slowly figuring out that an important aspect of the SOA is the ability to factor the ilities out of applications. The registry is key to facilitating this movement.