Thanks for all the input guys, you all raise good points. I will endeavour to recreate the author's work as faithfully as possible given the dimensions of the small screens on mobile devices. And as you say wallcraft, to 'gracefully' discard formatting which is not practical whilst reproducing the text itself. Over time I will be able to improve the way ZR renders epubs, FYI ZR does not use a html viewer control, I simply use a picturebox and my code analyses the documents which comprise the epub and determines hot to render the text and images. This is a lot more work but it gives me total control of how the result is rendered and to provide the user with formatting options.
Any and all input is most welcome, thanks again for your help.