Some features that would improve your app include the following:
•an inspiration gallery of high quality products created with your site
•options to create a magazines
•options to create books at sizes other than squares
•access to the marketplace function of blurb to sell and manage web store
•access to the online book store
•access to ebooks, especially your ebook maker. That's the biggest fail to me because people could create products for an mobile device on a mobile device which would optimize the design process.
•options for trade books
Good luck hope that helps! I love your site but your app falls way short! Hope you guys can get it together.