Some interesting news we got here. Saurik, founder of Cydia, is caching SHSH blobs for iOS 5.0.1. Check your Cydia account and you will surely find the 5.0.1 signatures there. In case you are new to this, an SHSH blob is a signature file verified against Apple servers to ensure that the device is running the latest firmware and why you need to save your SHSH blobs is to be able to downgrade to a previous firmware since Apple doesn’t allow that once you upgrade.
Apple decided that every restore of a device would need to be individually verified by their servers. This is clear within iTunes during a restore, by looking at the top information bar you will be able to see “Verifying restore with Apple…“
The process consists of a simple challenge / response protocol which uploads a partial digest of the firmware file to Apple, which then decided whether or not to allow the restore. The caching of the users SHSH effectively allows this process to be bypassed, verifying the restore via Saurik’s servers instead.
