Starting with iOS 5, Apple added some new checks to ensure people stick with the latest version of iOS. This made downgrading to iOS 5 impossible using SHSH blobs saved by Cydia or TinyUmbrella. But now, thanks to iH8sn0w’s iFaith, you can downgrade from iOS 5.1 or iOS 5.0.1 to iOS 5 custom firmware as long as you have APTicket + SHSH blobs saved for it.
