Amazon has started a service to sell books written in Japanese a month ago. I tried it by downloading a novel written by "Genyu Soukyu"（玄侑宗久） into my ipod touch.
I bought the e-book at 336yen. But, I can read it by using a library near my house with free. But, certainly, it is a convenient application because I do not need to bring a little big book with me. (This is the book（「中陰の花」） that I lent from the library.)
If I find an e-book that I think is worth of payment, I would use this service.
By the way, I have already a "kindle" but have not used it for a long time. This time, I tried to use it for the Amazon's new Japanese service, but unfortunately, I could not understand a way to change my kindle to the new service. I have to seek the way to use my kindle.