Surprisingly its not as common in Japan as you think. I was a Deshi for 3 years. It had nothing to do with slavery and I enjoyed every minute of it. It was mostly a religious experience for myself. I would like to see it become a more common occurrence because it clears the mind and puts you on that razor's edge of life. When I moved back to North America and opened my first dojo, I met a boy that was talented and trained very hard but didnt have the money to pay for lessons. When his parents moved, he stayed as a Deshi in my dojo. He understood that he had duties to do, and he also grew into one of my best students, not only of the sword, but also of Zen and the art of living.