While Java DB is Sun's distribution of Apache Derby, we do not maintain a separate users' forum for it outside of the Apache Derby users' forum.
So, the best place to post your Java DB questions is still the Apache Derby users' alias: derby-user.
The range of questions posed and answered there are truly fantastic, and interesting, some showing a great freshness of users.
Here's a recent...
Patrick Keegan describes how to use Java DB and Netbeans to create a personal data storage application using java DB and NetBeans.
(Java DB is Sun's distribution of Apache Derby.)
Edmon writes about his use of Java DB for persisting configuration properties used in Java EE:
Instead of using xml files for configuration properties I now use Java DB (previously know as Apache Derby) for the storage of configuration properties.
Java DB is a fully functional, yet small,
Java-based relational database.
It comes with Java 6 SE and it can be found (on Windows) under C:\Program...
Among those who'll be working on Falcon, I can see some superb Java DB engineers. Java DB is Sun's distribution of Apache Derby. It can also be found in the JDK, starting with JDK 6.
Knut Anders Hatlen writes about memcached user-defined functions (UDF) for Java DB on OpenSolaris.
Knut has also mentioned the recent release of Apache Derby 10.4.2. A corresponding Java DB release should be available for download soon. (Usually this happens immediately but we're all at a developers' conference for the next couple of weeks.)
For pure Java language innovation, take a look at Da Vinci Machine Sub-Projects.