I understand you're probably careful about which documents are included in http://www.princexml.com/samples/

Just curious as to whether it makes sense to have a forum for posting documents made with Prince?

For example, I've done several public domain texts from Project Gutenberg, like "Bartleby the Scrivener", the U.S. Constitution, etc.

How about the newly renamed "Samples, Tips and Tricks" forum? There you can post links to your documents, style sheets, or any other nifty things you've done with Prince.