The 'Zen in the Art of Archery' by Eugen Herrigel is fascinating book. Do not read it though, without reading the 'The Myth of Zen in the Art of Archery' article by Yamada Shoji (a freely available PDF). Hers is a direct link, and this is a google search.
The book describes the spiritual enlightenment of the author as he progresses
through kyujutsu studies in 1930s Japan.
The article, on the other hand, describes Herrigen as a person who came to Japan
to pursue all things Zen.
Not having a solid grasp on the language or the cultural context of his studies,
Herrigen sees Zen everywhere.
The fact that his teacher "...had no experience in Zen nor did he unconditionally
approve of Zen..." has no bearing whatsoever on Herrigen's perception of reality.
These two, are very relevant reading for people who try to make sense of Aikido.
They post warning signs all over the place.
Just replace kyujutsu with Aikido and Eugen Herrigel with your name, and you are all set.