Sometimes standards evolution can read a bit like a religious work! For example: in the beginning there was the word and the word was "events". Some of the Web Services architects looked at the word and came up with WS-Events. The rest of the Web Services world looked on that specification and found it wanting so begat WS-Notification. But this wasn't enough for some and they begat WS-Eventing. As with so many of the standardization efforts in those prehistoric days (WS-CAF vs WS-TX, WS-Reliability vs WS-Reliable Messaging etc.), this lead to confusion for the people, especially as none of these approaches were standards initially.
Fortunately WS-Notification eventually went to OASIS and became a standard, but it lacked the support of all major vendors. A modified version of WS-Eventing became a W3C Note around the same time but this is significantly less than a standards stamp of approval, though it did have some of the author companies from the other specifications involved. Yet more confusion abounded! Event notification ranks up there with security, transactions and messaging as core to most distributed system technologies over the past 4 decades. So it was no surprise that it would eventually come to pass that events would find their way into Web Services. Unfortunately because there is no single standards body for all Web Services work, that tends to lead to competing specifications (and standards). It's getting a lot better these days than it was back in the early 2000's, but it's still not perfect.
In an effort to solve the confusion around events all of the main protagonists (ourselves included) got together last year to form the Web Services Resource Access (WS-RA) technical committee within W3C. Part of that effort will standardize WS-Eventing. The timescale is fairly aggressive, with final standards due in June 2010 (which will include interoperability efforts).
But what do you do in the meantime? Events are important. Some vendors have implementations of one or more of these specifications/standards. What does that mean now that WS-RA is changing things? Well it definitely means that if you're already using a product based on one of the existing documents you will have to change something: backward compatibility is not a key aspect of the WS-RA effort. Of course change for change's sake won't happen, but some changes are inevitable (e.g., because the specs were broken or experience has shown a better approach). I'm sure some vendors will try to provide means to allow their existing products to continue to work with the next generation, but it is likely that changes will be driven right up to the developer. So be warned.
In terms of our own WS-Eventing offering, it's based on the older documents and is a community-only release. We're going to be working on providing a version based on the evolving standard and may have early access releases before the standard comes out (being on the committee helps!) So feel free to use what we've got for now in the community and watch the forums as we begin to work on the next generation.