Ken Kutaragi, President of Sony Computer Entertainment, has been saying that they may preinstall Linux on the optional Playstation 3 hard drive, to allow the PS3 to function more like a general purpose computer instead of just a console. He also says that it could run Windows or Mac OS X.
While technically true I think he may just be trying to generate buzz with the statements about Mac OS X and Windows, without any sanctioned support from either Apple or Microsoft. Apple traditionally has not liked people running its OS on non-Apple machines, and Microsoft most certainly wouldn't bring Windows to the PS3 before it brought it to the Xbox 360. Microsoft never allowed a full-fledged Windows to run on the Xbox, and there is no indication Microsoft will bring it to the Xbox 360 either. However, the comment about Linux is still intriguing. A PS3 running Linux and Linspire (along with the appropriate peripherals) could easily negate the need for a separate computer for many lower end users.