When hosting PCMech Live I have been asked more than a few times if it’s possible to run Linux on the PS3. The answer is yes, you can if you use the box as a development environment. Slashdot has an article on how you can put Fedora on a PS3 box with extra tips and tricks to get the most performance out of the unit.
Originally it wasn’t easy to get *nix to work on the PS3 but now it’s much easier than it was before.
So if you have a PS3 and were looking to do something different and interesting, there’s your project – with documentation. 
Why would you want to do this – would you lose the original OS?
You wouldn’t lose the original OS, but to do it you need a freshly formatted hard drive, so backup your stuff first. It allows you to boot to either the Cross Media Bar or into “*nix.” Doesn’t allow you to fully use the video card in the ps3 though.