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notcom a.k.a semaphore has released a new version of TinyUmbrella (5.11.01) to add support for the revised iOS 5.1.1 (9B208), that was quietly released for GSM iPhone 4 users yesterday.
TinyUmbrella allows you to take backups of SHSH blobs (ECID SHSH) that can be used to downgrade to older iOS versions even after Apple stops signing the iOS firmware file.
It can come in handy if you end up accidentally upgrading to the latest version of iOS.