Few of you know how the SHSH saving system works in Cydia, so I'll try to explain why you need them and how long it takes to save them. The SHSH is a file that contains the UDID of your terminal (unique for each iDevice) and is necessary to restore to old versions of iOS. Apple has implemented this system of SHSHs since iOS 3.x to block the possibility for users to restore to old versions of iOS. This is a method to fight against jailbreaking and decoding and unfortunately many iDevice owners suffer from it. These SHSHs can be saved in Cydia or on your computer and are absolutely necessary to restore to any old version of iOS if you have an iPhone 3GS/4, an iPad tablet or an iPod Touch 2G/3G/4G. If you have an iPhone 3G, you don't need SHSHs to restore to iOS 3.x.
Owners of iDevices have the option to let Cydia save these SHSHs by accepting a message called by saurik “Make my life easier” and once you accept it Cydia will always save SHSH for your terminal regardless of whether you have installed that version of iOS or not. Any SHSH saved by Cydia or TinyUmbrella appear in Cydia after 4-8 weeks from the save because that's how saurik thought the whole system to ease the workload of the servers. So if you save an SHSH now, it will only be displayed in Cydia in 1-2 months, so don't worry.
The SHSHs can also be saved by those who have NOT jailbroken their terminals, so don't be shy to save these SHSHs because one day you might need them.
