Here's one of the amazing pieces of news, one of iDB readers has noted that Apple still signing iOS 4.1 firmware for iPhone 3GS and iPod touch 2G.
I’ve found out awhile ago that Apple was still signing off firmware 4.1 for my 3GS , I’ve used SHSHit app to test this a few times now for the last 3 weeks and Apple is still signing it off..so if i’am right if you get a iPhone on 4.3.4/4.3.5 there is a very good chance that you could downgrade your device to 4.1 and have a untethered jailbreak..and you will be able to save those SHSH’.Another reports said that iOS 4.2.1 firmware can also be signed for iPhone 3GS, we didn't verify this ourselves so if you tried it please don't forget to feed us back.
If you have a device that supports iOS 4.1, we would recommend going back to that firmware temporarily, and saving your SHSH Blobs. This will now make it possible to downgrade your firmware, even when Apple isn’t signing it.[via]