Quoting DEV Team:
"The biggest mistake you can make (and it is a big one!) is lettings iTunes restore to the official IPSW youll lose the unlock and wont be able to go back! You must use Option-Restore, not just the Restore button by itself. Then navigate to your custom IPSW not to the stock one!"
Now, having in my case Jb and unlocked 4.01 my question is: what is meant by custom IPSW? I have saved all my shsh blobs from the virgin phone to Cydia etc, before jb and unlocking. I have subsequently downloaded firmware for 4.01 from apple site to my PC (is this not stock firmware?..)
When shift + restore under tiny umbrella server, what is one supposed to use as custom IPSW? This, I beliebe, is of general user interest, i.e. having secured a functional jailbroken and unlocked state, what must one do to back it up and safely return to it at any time. Or, alternatively, how to back up and revert to a pre-jb pre-unlock virgin iphone state using restore. ( So one can hapily and carefree venture and experiment into unknown teritory )
I know, the ingredients of the answer to my question are strewn among relevant sites, but so far, I have failed to find a concise step by step foolproof guideline.