I just got Gozo Shioda's book Aikido Shugyo and I must say that its nothing short of amazing! I must thank Jacques Payet and Christopher Johnston for translating the book to english. This is not only a very entertaining book, but it relays an extroadinary amount of valuable information that every Aikidoka should know.
This book alone could put to rest about eighty percent of all the threads in this forum. Shioda Sensei tackles issues that have plagued Aikido for its entire existence, such as its martial effectiveness, the way Aikidokas train i.e. competition, effectivness against other arts, and the list goes on.
One of the points that really struck me about Shiodas teachings was how he made the destinction between budo and sport and how many of todays various forms of martial arts have lost the martial aspect with the integration to sport. He explains very clearly how sport is essentially empty and meaningless in this context and how budo does not only involve the martial aspect, but it is also about every day life and should be integrated into everyday life to fully understand it.
This book is not only for Yoshinkan practitioners, it is a great resource of knowledge for all Aikidoka.