Although it seems most people don't consider PDF as a valid e-book format, I create PDF books for my Cybook (and for anyone else's of course). I try to keep the same page layout as in paper books, only a bit more condensed (minimal margins, small vertical spaces) and no left/right pages (the headers have book title, page number, chapter number and a pagebar and chapterbar). Have a look at
this example.
If a "real" e-book format, which allows reflowing and font/size changing, also allows this kind of formatting, perfect.