There's been a few hacks here and there for the PlayStation 3, but it looks like it's been really defeated by bad Sony programming. Basically, the hackers have found a way to calculate the "public" private keys to sign software to run on the PlayStation 3. How? Well, there's suppose to be a random number generated to help create these keys, but it seems like they use the same number instead of something, you know, random.
With some math, they were able to solve the unknowns in the equations and create their own keys to hack the boot loader to install Linux. While the video below doesn't show the PS3 loading Linux, it does show the person using ssh to get into the box and show off the CPUs. Tools should be coming in a month or so and I'm guessing some folks are getting fired at Sony.