Derby's arrival in Java 6 surprises me too (and I'm a Java 6 committee member)

Grumble grumble...

If I'd have been asked to vote, I'd have voted against it.  It has increased the JDK size and there was nothing about Derby that made it hard to work with after a download/install. 

Things in the JDK have a duty to have fairly stable APIs.  Is that true for Derby, or given the nature of JDBC is its jar not subject to stability?

I cast my mind back to Xerces' original inclusion in the JDK. The SAX api provided a similar boundary to developers. How did that work out?  I think the frustrations over package naming and the voodoo required to override the version distributed are worth considering when it comes to simply taking things from the Open Source world.