3GS iPhones can no longer restore to 3.0
As of this morning iPhone 3GS owners can no longer restore to firmwares 3.0 or 3.0.1. This is due to the fact that Apple has stopped signing these files and if you try and restore using one you'll get an error. So this means you should be very very careful until 3.1 is jailbroken because if you mess up your phone... you can only go up to 3.1 as of now. Additionally if you do not have your IBSS and IBEC signatures and you restore, you may never be able to jailbreak again.
iPhone 3G and first generation owners should still be able to restore with no problems.
via [Big Boss Blog]