When iOS 5 was released Apple incorporated some more security measures in itunes making it harder to downgrade. As of right now there is no way to downgrade to iOS 5.x. The creator of popular restoring software TinyUmbrella has released an update capable of collecting 5.0.1 SHSH blobs. If you are on 5.0.1 you might want to save the blobs for the future when they find a way to utilize them. You can download the software on their site here.
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