A hacking community member named KaKaRoTo has refused to offer his work for immediate download due to legal concerns, but instead has published the tools for others to build their own PS3 firmware.
It's only function right now is to trick your console into thinking the custom code you're running is official. It won't let users run homebrew programs or load backup copies of games, but no doubt someone will find a way to unlock one (or both, if someone really wants to homebrew) of those things in due course.
KaKaRoTo's blog hosting the information is currently offline since the publication of this story, but a copy is hosted on this hack-happy website and a video detailing the custom firmware still exists below.
The hacker states that "this custom firmware is really meant for future homebrew installation, and it will not allow piracy. I plan on keeping it that way." The cynic in us wriggles like a viper, but what do you think, readers?