There are some restrictions, which work out to basically one per customer (account), only those sold by Amazon (no third party sellers or used), and only until the number they've set aside for the promotion sell out (there's no end date posted on this promo, but I don't expect it to last very long). This time around, the deals page shows both the base models and the memory upgraded models for each of the Kindle Fires that are on sale, with links to the four models eligible all shown, so that it's easier to make your choice. Be sure not to use one-click, though - you need to go thru the full checkout process, so that you can apply the promo code above (and double check your total) before ordering, in order to get the sale price. If you are buying as a gift, be sure to click the box on the summary page for that, as well, so that the device isn't auto-registered to your account.
The Fine Print:
Limit one discount per customer, while supplies last. U.S. customers only. Discount valid on all versions of Kindle Fire HD 8.9" sold and shipped by Amazon. It does not apply to the same products sold by other sellers. Amazon reserves the right to cancel the promotion at any time. Promo codes may not be combined with other offers. If you return items purchased using a promo code, we will subtract the value of the discount from your return credit. Offer not valid with 1-Click ordering. Void where prohibited.