I bought one gift card, rather than twenty-five. The one gift card was not applied to my $2700 purchase, so I called Apple Support. After spending an agonizing amount of time with support, they corrected the problem, and applied the $100 to the purchase... or so I thought. Only because I was notified that you guys answered this question, did I check on the transaction. The $100 was removed from my Apple account, just like they told me. Yet, my credit card was charged the full amount. My $100 gift card evaporated into the ether! I'm on hold with Apple right now, as they try to figure out what they did with my $100. They can see the credit was there, they can see that they took it to charge against the computer, they just didn't subtract the $100 from the total. If you guys hadn't brought this question back to life, I would have been out $100 and not even realized it.
My recommendation is avoid this gift card at all costs. The frustration involved is NOT worth the mere twenty dollars credit with Best Buy. NOT WORTH IT.