Alice at Wonderland has a great post on the fact that the Sony PlayStation Portable game-carts have been compromised so that it's possible to copy the came from a cart to a PC. However, it's not possible to copy that back to a Memory Stick and load it into your PSP, because "the device will only run software that has been cryptographically signed by Sony itself."
Open and/or free always bests closed and/or expensive. Sony should have learned this when they chose ATRAC over mp3 – and look how much that cost them: far more than pirates ever could have. I guess this means no homebrew games running off the sticks then. *pout*
Update: Tim sez, "A crafty hacker on the ps2dev forums has homebrewed a psp binary using ps2 dev tools. He also figured out an exploit to run it off memory stick! Homebrew psp sooner not later!"