While many of us are thrilled that we finally have an unlocked bootloader on the Transformer Prime, and we even have our first custom ROM already, there is one vitally important caveat to know. If you have unlocked already, do not update with the .15 ICS release from ASUS.
IF YOU TRY A MANUAL UPDATE USING ONE OF THE STOCK ROMS AFTER UNLOCKING YOU WILL HARD BRICK YOUR TABLET
What this means is that for those users that have gotten past their various issues by manually downloading and installing the ROM updates from the ASUS website, or are changing ROM versions by copying the blob file, if you do this after unlocking it is a hard-brick, game-over. We now have multiple reports of this from some very experienced Tablet Devs and Users.
If you are going to unlock, install Clockwork, and do a NANDROID backup. You will NOT be able to use any of the ASUS published updates.
By pbrauer @ AndroidTablets.net
Sources - (XDA-Developers, AndroidTablets)