MuscleNerd has announced via Twitter that an upcoming version of RedSn0w will allow iPad 2 & 3 and iPhone 4S users to downgrade and restore (without upgrading to new iOS firmware) iOS firmware. That is, if you have saved your SHSH blobs.
If you have previously jailbroken your iOS device, then Cydia should have automatically saved them for you. This will be extremely useful for anyone who has upgraded their iOS software to a version that does not have a jailbreak. Downgrading iOS software can also be useful if you find that after upgrading Apple has made some changes that you dislike and would prefer to return to the previous version. In this case, you would need to save your SHSH blobs using TinyUmbrella.
@MuscleNerd has not mentioned when the updated version of Redsn0w will be released to the public.
We will keep you posted.