It completely bypasses our system: we earn $0 from Lulu sales. (It was added by Dr. Peng. Leanpub authors own the copyright to their work, and can sell it wherever they want.)

That said, having used Lulu myself in the past (back in 2006), Lulu pays good royalty rates on print books and ebooks, and we recommend that all our authors consider using Lulu or Amazon CreateSpace to produce a print book once their book is done. If you search "Leanpub" on Lulu, you'll see a handful of Leanpub books there.

To help our authors produce print books, we have two features:

1. Print-ready PDF export. Click a button, get a PDF with proper page numbering (alternating sides), chapters always starting on the right page, no cover image (since Lulu and CreateSpace have wraparound cover upload features), etc. I think that most of our authors who have print books, including Dr. Peng, went this route since it's a lot easier than the second choice.

2. InDesign export. Click a different button, get InCopy (ICML) files. These can be given to a designer who is good at InDesign, and he or she can make a beautiful custom-designed book. Our InDesign export is pretty basic compared to the print-ready PDF export, but our hope is that it's a better starting point for a designer than a Word document with a bunch of formatting that they need to throw out.

For us, making the print book production process as easy as possible just adds to the value created by using Leanpub. We want to create more value than we capture, and this helps with that...

Cheers