A reminder to save your 4.2.1 SHSH blobs while you still can
UPDATE: It has been brought to our attention that Apple is no longer signing 4.2.1, if you didn't save your SHSH for 4.2.1 by now, you will never be able to. If you are on 4.3 and looking to downgrade, you will unfortunately have to wait until a new jailbreak tool for 4.3 is released.
As you know, 4.3 firmware was released to the public this week. Historically, Apple has had a buffer where they continue to sign the previous firmware(4.2.1 in this case) for a few days after the release of the new firmware. After they stop signing the firmware you will no longer be able to save your SHSH for 4.2.1 for the rest of eternity! So make sure you back up your 4.2.1 blobs now, 4.3 is not currently jailbreakable so if anything goes wrong with your device and you have to restore, you will be SOL without your blob. Go to the Firmware Umbrella website and download the latest version, connect your device and click "Save SHSH" take a look at our TinyUmbrella tutorial if you are unsure of what to do.