I just uninstalled the beta, installed the release, and typed my registration code every which way, all caps, all lowercase, and a combination of the two... deleting my .cfg file to reset the game to demo status every time (thus requiring that I re-enter my registration key). Every time, the key worked.
In all likely-hood, the "problems" that everyone has been encountering is the fact that they're so excited to play the full game that they're simply typing the code in too quickly and fat-fingering the result.
Everyone just needs to stop, take a deep breath, examine their codes, and enter them one key at a time... maybe even taking a break between each letter/number. It's okay people, you'll get to bask in the glory that is Book II. Just have a little patience.
As a computer tech/IT person, I can't tell you how many times people absolutely insist that they've entered in the correct password, and yet when I do it for them, it works like a charm. Then I get accused of some voodoo-mumbo-jumbo.
*** Edit ***
There's no registration server (nor do I remember BW ever mentioning one). I've installed it on a laptop with no internet connection with no problems.