I've got email saying Mastercard Marketplace will have $10 off a $20
Starbucks gift card thus totally making it $11.99 for $20.
Remember it will be activated based on 'check-in'. My rough guess will be 10
You have to register your master card before you try to reserve.
Quantity is 3600. I think it will be gone less than hour
Link: http://www.marketplace.mastercard.com/overwhelmingoffer/index/o