I just found news of this at
http://www.videogaming247.com/2008/04/25/xbox-360-sales-pass-19-million/
According to this Eurogamer report, Xbox 360 sales have now passed 19 million globally.
The new came as part of a general Microsoft first quarter financial release yesterday, which showed the Xbox division had increased sales 68 percent for the past three months year-on-year.
Xbox 360 sales were last confirmed at 17.7 million in January.
Is this reliable as it doesn't agree with what's on the site here.