Compiling the Arduino Leonardo bootloader (aka Caterina) is a required step in making your own Arduino Leonardo-compatible board available to others. Steven Casagrande has written this post detailing what you need to do in order to make your derivative board valid for sale.
Via the contact form.
The link is broken – is there a new URL available please?
@james it looks like it’s now at http://archive.is/h1jf0
Wow