A new version of redsn0w is now available for download thanks to the iPhone Dev Team. The update focuses on the ability of the iPhone 4S, iPad 2 and third-generation iPad to downgrade their iOS versions with the use of saved SHSH blobs. redsn0w 0.9.11b1 allows iPhone 4S and iPad 2 owners to downgrade to iOS 5.0.1 or higher and iOS 5.1 for third-gen iPad owners. While all A4 iDevices have been able to downgrade prior to this release thanks to the limera1n bootrom exploit, A5 iDevices weren’t as lucky.
A great addition to redsn0w that comes in this release is the ability to downgrade your iOS version directly in redsn0w without having to use iTunes at all. This is done by navigating to Extras > Even More > Restore, and can, of course, only be done with SHSH blobs for the appropriate version of iOS to which you wish to downgrade. Unfortunately for unlockers, this downgrade method will update your baseband, so it should be avoided until a workaround is developed. The only unlockers that are safe from this are those that used the now-patched SAM method to unlock.
Lastly, this new redsn0w release is not entirely stable, is not recommended for regular use, and should only be used for the new downgrading feature. The iPhone Dev Team is currently working out the bugs and other issues in this version and should be releasing a more stable update in the near future. redsn0w 0.9.11b1 is available for download now for OS X and Windows.