iH8sn0w is a well known iPhone hacker. He is credited for developing jailbreak tools like Sn0wbreeze, iREB and iFaith. Yesterday he disclosed a new discovery of his via Twitter. The exploit he has discovered will allow users to downgrade iOS 5.1 to iOS 5.0.1 on iPad 2 and iPhone 4S.
This exploit will prove to be very useful. The iPhone 4S and iPad 2 can not be jailbroken on iOS 5.1, but they can be jailbroken on iOS 5.0.1. This exploit will allow users to downgrade iOS 5.1 to iOS 5.0.1 on their A5 based devices, meaning that those users who mistakenly upgraded their devices will have another chance at jailbreaking their devices. Do remember that if you didn't save iOS 5.0.1 SHSH blobs, then there probably won't be any way left to downgrade firmware.
iH8sn0w has also said that this exploit will function with A5X based New iPad as well, but only when Apple releases a new firmware update for it. He is yet to reveal finer details about this exploit, we'll update you as soon as he announces something.