UPDATE: Sorry for my blathering, everybody. If the site messed up for you after registering your copy of FF13, you can still retrieve your code by performing the following (NA users):
1) Go to http://member.square-enix.com/na
2) Log in with your Members account.
3) Click the "Features" tab in the general menu at the top of the screen.
4) Click the "Final Fantasy XIII" section (either the title link or the picture will work).
5) In the left-hand menu along the left side of the page, click the "Bonus Codes" button.
6) If you registered a copy of FF13, there will be a link for whichever system for which you registered.
I apologize if this is not the correct topic under which to post this finding, but I felt it was important to provide an answer in the same topic under which I asked the question. If anyone needs help with these instructions, I will gladly answer any PMs.
Edited, Mar 11th 2010 7:48pm by PLDXavier