Science Friday (NPR) just did a piece on it recently.
http://www.sciencefriday.com/program/archives/201103114
To me, it seems like one step forward and one step backwards.
It's better for the environment than having warehouses full of paper books that have to be physically transported to the retailers and consumers. However it's not as good as just simply forgoing paper entirely and using an electronic reading device. In fact, it's almost the opposite of an eBook, because the book is already in an electronic format in the Espresso machine's database, and then converted back into paper by the printing process.