Wait. I thought Nintendo wasn't traded on the US Stock Market.

It's traded as an ADR, which according to wikipedia:

An American Depositary Receipt (or ADR) represents ownership in the shares of a foreign company trading on US financial markets. The stock of many non-US companies trades on US exchanges through the use of ADRs. ADRs enable US investors to buy shares in foreign companies without undertaking cross-border transactions. ADRs carry prices in US dollars, pay dividends in US dollars, and can be traded like the shares of US-based companies.

Each ADR is issued by a US depositary bank and can represent a fraction of a share, a single share, or multiple shares of foreign stock. An owner of an ADR has the right to obtain the foreign stock it represents, but US investors usually find it more convenient simply to own the ADR. The price of an ADR is often close to the price of the foreign stock in its home market, adjusted for the ratio of ADRs to foreign company shares.

NTDOY pretty much trades like any other stock, but the timezone it's traded is EST as opposed to Tokyo time. This means that if something happens in Japan, there isn't much you can do except wait til the American markets open. NTDOY trades at 1/8 a whole share, since NTDOF the full share is pretty expensive.

E-trade is going to allow trades on foreign stock exchanges soon, so perhaps Americans will be able to trade on Nintendo directly on the Tokyo Stock Exchange in real time.