Thanks for the write-up, David. I will let Ordbrand know and we will see what can be done.
Students have a number of off-line ebook reader tools to choose from, iBook on the iPad or iPhone, FBReader on Android, Lucifox on PCs with Firefox to name a few.
EPUB is the standard vendor neutral format chosen by the international publishing organizations for digital publications, see the International Digital Publishing Forum, http://idpf.org/ , and it is supported by a large number of publishers and tool creators. Publishing is often done to a number of formats at once. Dealing with conversion is easier if the document is well structured and according to format specifications, i.e. it helps to be a bit strict, but when used one should strive to make it less obvious.
EPUBs reuse existing web standards , adding a navigational spine to the content, which helps machine reading - think text-to-speech of a multimodal text in the correct order, and a packaging method - EPUBs are regular ZIP archive files, just with an extension of .epub rather than .zip.
The current Lucimoo export tool allows only a single book to be exported. Another tool by Ordbrand is Luciwik EPUB/OPDS for Mediawiki (the software which runs Wikipedia). Luciwik lets you export a single article or to select several articles for export to EPUB. You can see an example in the left hand menu at http://far.no/index.php?title=Askeladden_og_de_gode_hjelperne . Luciwik also adds an Open Publication Distribution System book catalog to Mediawiki, allowing discovery of new books either from a web page or by adding the book catalogue feed to ebook readers like Lucifox or FBReader. Perhaps it will be possible to include this functionality in Lucimoo later.
The Moodle Book module itself needs a bit of love, e.g. you cannot import a book directly by simply selecting an EPUB file as a resource file and have Moodle/Lucimoo import and display it. To make this happen requires changes to the Moodle Book module itself by its developers.