So I ran into a problem redeeming my destrier beret. I figured out the solution so I thought I'd share it here just in case any one else runs into the same problem.
The directions on the SE Support Center are incorrect. They tell you to redeem the code using the PlayOnline Viewer, but the viewer gives a message saying you must do it on the SE account management web site.
I did some poking around and finally figured it out. Once you log in to the SE account management site do the following:
1. Click Select Service
2. Click PlayOnline/Final Fantasy XI
3. Click Add a Service Account
4. Enter the redemption code
5. Select the account you want to apply it to (If you have more than one FFXI account)
6. Select the character you want to give the beret to. Keep in mind it will only go to one of your characters, so choose wisely!
That's it! Oh wait, then go pick it up in game from a Festive Moogle. I almost forgot that part.