I'm reading A New Kind of Science by Stephen Wolfram currently. This is sold as an application rather than ePub, no doubt due to the formatting control required by the publisher and perhaps its size of 1200 pages. However, one misses out on the reading modes provided by iBooks and other features. There is room therefore it seems, for great improvements that no doubt will come.
I have a short story on the iBookstore - good fun.
All the best (happy new year).