Passing along an interesting project link  http://code.google.com/p/openpub/wiki/OPDS. From their site:

"This document describes the Open Publication Distribution System (OPDS) an application of the Atom Syndication Format intended to enable content creators and distributors to distribute digital books via a simple catalog format. This format is designed works interoperably across multiple desktop and device software programs for acquiring and consuming eBooks ("Reading Systems"). The focus of this document is to outline the requirements for preparing catalogs for use by compatible Reading Systems; formal compliance requirements for Reading Systems will be documented elsewhere. This application of Atom was initially defined and implemented by Lexcycle for the Stanza application."

It answers the long-standing question of what format to use when creating content for computer-based or computer-mediated learning environments.