Guys I just wanted to post my story:
1 console banned from long time ago (during Halo 3 beta w/ backup of Crackdown disc)
1 clean console
I only play legit retail games on the clean console.
After reading all the threads, pages and pages, I just decided to try and see what happens.
I hadn't logged onto LIVE with the clean console in months, so I had I to update the console a few times (2 I think). Anyway, it's definitely up to date. During this time of course, my sole HDD was on the clean console.
After the update, I plugged my HDD back into my banned box to boot up a backup, and of course it tells me that I have to install the latest update in order to even play this backup. Never had this before, so it was definitely due to the update on my clean box (something must have transferred onto the HDD).
Anyway, I get on, and everything is fine. So I make some progress and save. Then I switch back to the clean console and boot up a retail game again. But the key thing here is that I make some progress and save the game on the clean console, before logging into LIVE. I never log into LIVE automatically. I was able to update my gamerscore no problem, after logging into LIVE.
Here another thing, I was playing backup of game X, and then bought game X retail later on. I always make progress and save on the clean console before logging into LIVE. So that the console ID of the gamesave would be one that is not blacklisted (banned).
I have been switched back and forth all night, from clean to modded(banned), and so far no corruption. Of course I will update if anything changes.