According to a pressrelease from Sun, they have released a database based on Apache Derby. The DB called Java DB.
The latest version of Sun Java Enterprise System (release 4) now uses Java DB, and it is the default database for development with Sun Java System Application Server. Further it is the default database for Suns Portal server.
The same day Sun released a plug-in for NetBeans 5 for connecting to the DB.
Quite cool I must say, I looked briefly at Apache Derby at the past and it seems to be a quite capable RDB.