About two points I tried to improve.

Hi, Homme.

Your cesium-terrain-builder project is great idea!
I have be looking for such a tool.
Thank you!

I e-mail in order to contribute to the project.

I have two problems using ctb-tile on Ubuntu 14.x.
Finally, I was able to fix.

One is that top level terrain directory is created 666 attribute. 
So, root user can look under the directory. 
But other user can't.

The another is that terrain data always has no child flag.
The reason is that simple mistake in Bounds.overlap() method.
Look the fix.

Best regards,
Kyosho.