Market Research company NDP Group released sales numbers of the Xbox 360 in the United States.

According to NDP Microsoft has sold 325,902 Xbox 360 consoles in North America. In the same timeframe MS sold 556,221 original Xbox consoles when it launched.
Call of Duty 2 is the bestselling Xbox 360 game so far.
Considering the high price of the Xbox 360 compared to the Xbox, the numbers are decent. There is still extreme demand for Xbox 360s in the US. MS has just to put them on the shelves. More sales statistics on TeamXbox.

No there is a completely different situation in Japan. Apparently Microsoft only sold 62,100 Xbox 360 consoles in the first 2 days in Japan. Microsoft apparently made 159,000 Xbox 360 consoles available for Japan. So only 40% are sold yet. Microsoft sold more than double of original Xbox consoles when they launched that one in Japan.
Munetatsu Matsui, editor-in-chief of "Famitsu Xbox 360", says: "There is just one reason for the slow sales -- the postponement of the launch of the 'Dead or Alive 4' game". More details on Reuters and on DigiTimes.

By the way, the Xbox 360 bundles offered yesterday at GameStop are now sold out again. The ship again earliest 31st of January 2006.