COD Modern Warfare 2: $20 Credit at Amazon

 I ordered Rock Band 2 from Amazon and, as if I needed an excuse to pre-order COD: Modern Warfare 2, this popped up:

Get a $20 Video Games Credit
Order Call of Duty: Modern Warfare 2 and get $20 off a future video game purchase. The promotional code will be placed directly into your Amazon.com account within 2 business days after the product ships. Offer valid for a limited time and only when shipped and sold by Amazon.com. This offer will be extended to all existing pre-orders. Amazon reserves the right to change or terminate this promotion at any time. Limit one per household.