iFaith is the amazing application that pioneered iOS 5 downgrading.
In case you aren't familiar with iFaith, it's a Windows application made by iH8sn0w
that dumps your SHSH blobs and APtickets locally so that you can make custom signed restorable firmwares. iFaith was the first application that allowed you to make a signed '.ipsw' file for iOS 5. If you like what you're hearing so far, you might be interested in hearing that