Similar to NYTSKY I have visited japan. In my couple of short stays(2 weeks at a time) I have been blown away by the cleanliness/friendliness of the place. Obviously, as a car fan I visited many tuning shops and the TAS, which certainly was enjoyable. I also loved the food and the quirky things you see on a daily basis. I have also visited and enjoyed Mt Fuji/ Hakone and caught the shinkansen to Osaka for a few days. All great experiences.
I would love to spend 12 months in Tokyo but not being able to speak the language is a major barrier. It is not too bad as a tourist because a lot of japs can understand a little english or you can point etc. However other than perhaps teaching english what can a foreigner do with regard to employment?
In response to the title of the thread, I would say that my motivation to come over for an extended stay is to enjoy the massive cultural difference and to feed my addiction to high performance japanese machinery.