I'm the same way about the progress thru the book, but found the slider in eReader worked OK for me. It could be because of how small the iPhone's display is that I found it an acceptable way to show it.


Looking at screenshots of iBooks, such as the first one in this review:
http://www.tipb.com/...view-ibooks-ipad/

It doesn't look like they reinforce how far along you are in the book. Looking at the image, keying off of the spine area and the pages visible on either side, it appears as if they were exactly 1/2 thru the book, though based on the page count it's really 1/10 of the way thru.