Apple has ended the window for installing iOS 5.0.1 on your iPhone, iPad, or iPod touch, reports *****i.
A5 devices are now immovable from iOS 5.1 if they have been updated until a solution for downgrading can be found. SHSH blobs will not do you any good for downgrading an A5 device at this time.
Please be extra careful not to accidentally update to iOS 5.1 via iTunes or Software Update on your device. If you do update you may lose the ability to jailbreak for quite some time.
A4 devices with saved blobs can still be downgraded as usual.
The inevitable window has finally closed. Apple has officially ended the signing period for downgrading back to iOS 5.0.1 for all iDevices. A5 devices are now immovable from iOS 5.1 if they have been updated until a solution for downgrading can be found. SHSH blobs will not do you any good for downgrading an A5 device at this time.
A4 devices on the other hand, which support iOS 5.0.1 firmware, can be downgraded only if you have a custom firmware, which has been signed by iFaith or stitched by redsn0w using your APTickets. These firmwares will still downgrade A4 devices because A4 devices contain a bootrom exploit known as limera1n. This is the big difference that sets A4 devices apart from A5 devices as A5 devices do not have a bootrom exploit at this time.
A5 devices updated to iOS 5.1 do not have an untethered nor tethered jailbreak, meaning if you’re at iOS 5.1 then you are now jailbreakless until a new jailbreak is created for iOS 5.1. A4 devices have the choice to either downgrade back to iOS 5.0.1 or have a tethered jailbreak on iOS 5.1 with the latest redsn0w (0.9.10b6), which was released yesterday. I wouldn’t recommend the tethered jailbreak on iOS 5.1 because many tweaks and Cydia packages are not compatible nor programmed to work with iOS 5.1 yet.
If you have an A5 device currently jailbroken on iOS 5.0.1, this is your only prerequisite: be very careful what you install on it. If anything goes wrong, forcing you to restore, you will not be able to get back on iOS 5.0.1.