Does anyone know if there is an online platform for selling e-books which also comes with an iPad (and PC/Mac) reader app for purchased content? The reason being mainly to prevent people copying and passing around the purchased material (as they can do with PDFs), as well as presentation (ie. how the free books, iBooks, and Borders Books iPad apps work). I've looked around and various e-commerce & bookshop packages and services, but haven't found anything which offers more sophistication than simply dowloading PDF files. Surely someone's already come up with an online bookshop + iPad app combination?