There was a very nice spanish community that would scan/ocr books and convert them into epubs. They had very high standards and their forums were full with epub documentation, best practices, boilerplate/skeleton files, scripts, etc. To the point their curated epubs were better than those of some publishers.

It all died when one of the founders was arrested.

Edit: it seems my information was incorrect, the site's owner sold it and the new owners wrapped the download links with malware and closed the forum. Users left and the site closed.