Putting aside any complaints about whether or not Apple should have given people that $100 gift certificate, we've been seeing reports of people getting a message that there's $0 balance left on their cards when they go and actually try and use the money. And by reports, we include myself, Jason Chen, because I ran into this problem last night. After reading up on the Apple Support Forums, it seems the solution is to apply for ANOTHER gift card (link), generate a new number, and use that one. We're not sure whether Apple's giving out the same number to multiple people or what, but this seems to work.

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