Apple have released an ePub guideline - Recommendations - they call it. Thankfully just one and a half pages on preparing ePubs for the iPad. Mostly it addresses their particular set of device limitations.
The iPad is a game changer, insofar as the rendering and presentation quality is excellent. The paper page metaphor is too strong for my taste but for a paged reader, the CSS implementation far ahead of ADE. This means their is no need to create crappy CSS for a particular device; and the XHTML and CSS is more future ready.
We have a standard test-book which has to be stylistically dumbed down for the quirky display properties and bugs in ADE and those devices that inherit ADE. Things are move lively on iPad. The sample screen grab here shows images sized by CSS and floated left.The recommendations are mostly common sense and straight-forward.There are a number of screen-grabs of our Trade test book included showing the presentation of various structures.