Having same problem. Posted to support page last night and got this response this morning:
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Sorry to hear that you were not able to redeem your card. I understand how frustrating this could be.
Apple is currently working toward a resolution for the issue you have reported. You will receive an email after the matter has been investigated and further information is available.
Thank you for your patience. Apple wants your iTunes experience to be as enjoyable as possible.
Sincerely,
Mini
iTunes Store Customer Support
http://www.apple.com/support/itunes/ww
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Anyone enjoying themselves??