I think I will brick my Bionic if I try to revert to ICS from the JB update, but I want to confirm with others more daring with their phone than I.
Why revert? Without Root access, I cannot get Titanium backup to restore everything I moved to the SD card. I want to reload ICS with RSDlite, restore everything with titanium, then do the upgrade to JB.
I think the fatal flaw in my plan is moving back a version. I think this bricks the phone.