The original PSJailbreak device cost over $100, but soon an open-source variant was released, giving would-be jailbreakers a chance to open up their systems using devices they may already own, such as Dual Shock controllers, Sansa players, iPods and USB Dev boards.
PSDowngrade software can be installed on pre-existing PSJailbreak devices and will downgrade your firmware to 3.41, or any other previous firmware.
For those that want it, you can downgrade to 3.15 and get back OtherOS Linux support.
The devs also say: "[PSDowngrade is] completely safe to use, and does not void your warranty. PS Downgrade is completely undetecable by manufacturer, there is no history or log of your downgrade."
PSJailbreak + PSDowngrade costs $125.
Check it here: PS Downgrade