FYI - here's the email you get when the free period is ending and you need to cancel your free shipping program:
Your Premium Shipping Plan free trial is about to expire.
Dear Customer,
Your free trial for the Premium Shipping Plan will end on April XX, 2013. At that time we will automatically charge you for the annual cost of enrollment using the payment method you provided to us. As a thank you for your enrollment, we will send you a $25 Gift Card that will arrive approximately 2 weeks after we process this charge.
As you know, the plan allows you to receive free Express Next Day shipping on each American Express Gift Card order placed for one full year. We hope you will take advantage often of this service.
If you wish to cancel your enrollment before the free trial ends and you are charged the annual enrollment fee, you may do so by logging in to your account at americanexpress.com/gift. You may also call 1-877-297-4438 to speak with a Customer Service Representative 24 hours a day, 7 days a week. Thank you for your business.
Sincerely,
American Express Customer Service
The whole program seems to be targeting people who buy them on behalf of others - like a corporate purchasing department. They reward the people in the department via BigCrumbs and this $25 card.