Two days ago Apple released iOS 5.1.1 for iDevice owners and kept the SHSH signing servers active for the old iOS 5.1. Because those servers are active, you can still save an SHSH for this version of iOS and you can restore to any iDevice via iTunes. If you want to restore then access this page, download iOS 5.1 for your iDevice, open iTunes, connect the terminal, backup/save the data, then holding down the shift (Windws)/alt + option (Mac) key, click on the iTunes Restore button, choose the ipsw for iOS 5.1 and wait for the restore process to finish. After everything is finished you will have iOS 5.1 installed on your iDevice and currently you can follow this process to restore ONLY iOS 5.1 to any iDevice without using SHSH.
If you want to save a SHSH then download TinyUmbrella from here, connect the device, uncheck Request SHSH from Cydia and press Save SHSH. Alternatively, you can use the iSHSHit application from Cydia. Unfortunately, these procedures can only be done in the following hours/days, because Apple can stop signing SHSHs for iOS 5.1 at any time, so I recommend you to hurry. If you save the SHSH for iOS 5.1 now, then in the future you will be able to downgrade to this version of iOS on any iDevice using redsn0w.
