Does one exist or is one in the works? I have looked at a few of the examples, but a deeper more detailed understand of what is going on would be nice. It would be nice to have something similar to the examples in the Starter.pdf.
I know everyone is busy though. 
A guide would be nice, but it can’t cover all interesting topics. Therefore it is more important that javadocs for the GUI are written. The examples are only helpful if you want to do exactly the same. If you want to use for example particle effects with WidgetViewports there is no documentation to read.
jME is great but the poor javadocs could be a reason not to work with jME. In my opinion it is not possible to program a game with jME without having a look all ten minutes in the source code. It’s a pity.
The jME GUIs (ui and widget) are in a bit of flux. This is shaky ground at the moment, and needs to be solidified into a single vision.