Enterbrain reports that the Wii system has, as of November 23, sold 7,000,000 units in Japan. To compare, the GameCube has sold 4 million in its home country (according to Wikipedia), and the DS has sold -- oh wait, that one doesn't make the Wii sales sound as good.
Helping to drive the Wii sales last week was Animal Crossing: City Folk, of which an astonishing 303,204 copies flew off of Japanese store shelves in its debut week. If we were feeling snarky about Animal Crossing, we'd say that between that and Chrono Trigger, it was a good week for ports. But that's mean.