Sony announced today that the PSP console cumulative worldwide sell-in units of PSP (PSP-1000, 2000, and 3000 series) reached a total of 50 million units.
The 50 million is a sell-in number, which I suppose means that Sony sold 50 million PSP into the retail channel, but there are not 50 million PSPs in the hands on gamers yet.
The Sony PSP made its debut in December 2004 in Japan, March 2005 in North America, May 2005 in Asian countries and regions, and September 2005 in Europe/PAL territories.
In comparison the Nintendo DS already sold 28 million in the United States alone. The DS is actually close to reaching 100 million units world-wide pretty soon.

Still the Sony PSP is actually in better shape than the PS3.

Photo taken from our Sony PSP Gadget Model Gallery.