Last night I successfully downgraded my iphone 4 from 5.1 to 5.0.1. I found there are many ways to do this once you have a saved shsh blob for 5.0.1. One of the ways I found to do it for windows based machines was a program called iFaith. I also found a way to do it with redsnow for users like me that don't have windows and are on mac machines. http://jailbreakhow.net/downgrade-5.1-to-5.0.1-5.0-4.3.3-4.3.5-iphone-4-3gs-ipad-2-1-ipod-touch-4g-3g/ The URL has both methods on it. Hope this helps out someone.