TinyUmbrella allows you to take backups of SHSH blobs (ECID SHSH) to let you downgrade to older iOS versions.
He has provided the following information on his blog:
TinyUmbrella now has support for saving 5.1 SHSH for Apple TV 3 and the iPad 3 (all versions). As of now we still cannot restore them but we are working on getting that working from a bunch of angles. I’ll let you know more when I do.
SHSH blobs of iPad 2, the new iPad, Apple TV 3 and iPhone 4S are not useful currently as they can’t be used to downgrade to older version, but it is still a good idea to save SHSH blobs as they could end up being useful in the future.
You can download the latest version of TinyUmbrealla from Semaphore’s blog.