Sony announced yesterday that the worldwide life-to-date sales had exceeded 21 million at the close of the 2008 year. These numbers would put it past the lifetime-to-date sales of the Nintendo Gamecube(though in the North American and Japan regions, it still trails it), and puts it just a few million consoles behind Microsoft's original XBox.
Almost exactly a year prior, Sony had announced that they had sold 10.5 million consoles since launch. This means that PS3 numbers have doubled over the past year. The console sales were likely spurred by Sony's stellar 2008 software line up, including Metal Gear Solid 4, LittleBigPlanet, and Resistance 2.