Great idea. I bought Uncharted 3 and have a $20 coupon so I'll use it to get MW3 + 4000 MS Points for $90 - $20 = $70 then I'll get a $15 gaming coupon. $15 kind of is a crappy deal because previous deals were for $30 and $20 for Batman Arkham City and Uncharted 3, respectively. But I guess better than nothing.
Actually they don't need a promo to push MW3 which is why you're only getting $20 off the 4000 points. The $15 is generic for just spending $40. I don't even think Amazon is doing promo credit directly on the game. But really you're getting $35 for buying both. Also if any one plans to do this, make sure you are signed up for SYWR (Save Your Way Rewards) because it's required, and it's free.
For the Skyrim fans in here, there is an even better deal. Wait until Friday (11/11/11) and buy MW3 and Skyrim, and you will be rewarded with the $15 gaming coupon plus an additional $35 gaming coupon for spending $110. That's a total of $50 which is almost another free game. They have to be purchased on the same receipt. If you can't wait on MW3, but it Tuesday and just do a rebuy when you get Skyrim.
Also thought I would add all the promo credits available this week in case any one is looking to get these games and MW3.
James Bond Goldeneye 007 Reloaded - $15 credit
Uncharted 3 - $20 credit
Lord of the Rings: War int he North - $20 credit