In general "data binding" refers to linking up UI elements and models so that a change in one will automatically affect the other. Using a data binding framework makes this easier because you don't have to write your own listeners and validators and converters. There are several data binding frameworks available for Java developers, including a new one from the Eclipse project called JFace Data Binding.
Originally the Eclipse one was going to be finalized in version 3.2 of the Eclipse Platform but it looks like it needs a little bit longer in the oven. In a posting to the Platform UI committer's list, Boris Bokowski writes:
"We have decided to *not* publish the data binding framework as official API for 3.2 because it has not yet received sufficient review and/or adoption. In particular, we were not confident that the listener notification API was sufficiently stable."
So, Eclipse 3.2 will include the data binding framework, and people are encouraged to try it out to shake out any problems, but with the caveat that it may change in the next release. This makes a lot of sense, because the best APIs are ones that have been tested and used in real applications. Saying something is "official API" locks you into backwards compatability.
Another reason for this change might be the desire of Java developers not to have so many binding frameworks. With the API deadline removed, perhaps the players can sit down and discuss a common framework.