ShuBook is, indeed, a Stanza replacement. Even the interface is quite familiar.
I'm on an iPhone 4, however, and still running iOS 5, so what ShuBook has replaced is eReader. I shuffle between Stanza and ShuBook as I am typically reading two books at a time and it is easier to switch readers than switch books!
Dreamnine, I'm surprised that you found "nothing" to like in ShuBook! I can think of two things right off the bat that make it much better the iBooks: customizable color themes of text and background-- and NO animation on page turning. There are plenty more, but those are just two of the biggies.