During the last evening on the Dev Team blog, a article through which the team wants to warn iPhone 3G/iPod Touch 2G users about the implementation of a security measure in the new iOS 4. It seems that with the release of iOS 4.0, Apple implemented the need to use SHSHs on the iPhone 3G/ iPod Touch 2G and users trying to restore to iOS 4.0 are blocked due to this new security measure. Cydia already saves SHSHs for these 2 devices as well as for the iPhone 3GS and if you want to use them, you must use the same downgrade tutorial already available for the iPhone 3GS.
Those from the Dev Team say that this restriction with the use of SHSHs can be easily overcome using redsn0w/PwnageTool, but it's easier with the SHSHs from Cydia. You can restore to iOS 3.x without problems because there was no need for SHSHs, but for the new iOS 4.x it seems that you need them.
