One of the things I find helpful is to open up the contents pane on some of my books to understand the flow of the text and where I am reading in relation to it. In the Windows Logos engine, the current section is highlighted and it moves along as you read changing to a new sections as you arrive at them. In the Mac version, the highlighted section is static and does not move with your reading.
I know this is a minor enhancement, but can I ask please with sugar on top to add this in a future version? A small thing like this makes an ebook so much intuitive. 