Amex Offers has a iTunes offer that showed up today. In my account it shows as a $5 statement credit by when you spend a total of $5 or more on iTunes. On SlickDeals, mangust and others report that they are seeing a $10 credit offer for a $10 spend.
I don’t see the offer the Amex my business credit cards that I have, the Gold and Platinum.
The offer can only be added on to your card by logging into your account and is not available through Twitter. Use the multiple browser trick if you have more than one card on the same online account.