Reuters reports that Microsoft has sold 600,000 Xbox 360 consoles in the United States since its November 2005 launch. Data comes from the NDP Group which measures and projects nearly two-thirds of all US retail sales.
From the article: "The Xbox 360 debuted to much fanfare on November 22 in North America, where the unit has been in short supply. Analysts, video game publishers and retailers have said shipments during the key holiday season fell short of expectations."
As expected, the system has not been selling well in Japan up to this point either, but Microsoft has confirmed its target of selling between 4.5 million and 5.5 million 360 during the current fiscal year ending June 30 of this year.