Amazon Partners With Twitter To Make It Easier To Buy Stuff Through Twitter
Here's how it works:
First, you have to link up your Twitter and Amazon accounts in Amazon's social settings section. Then, if you're checking out Twitter and you spot a tweet with an Amazon link for something you want, all you have to do is reply to that tweet with the hashtag "AmazonCart" for that item to be placed in your shopping cart.
The item will be saved, but not ordered until you actually review your cart and you'll also receive a response tweet from @MyAmazon to tell you whether the product was successfully added (or whether it was out of stock).
The idea for Amazon is that if you can instantaneously save a product that you're interested in, you're more likely to buy it, since otherwise you might forget or not want to go through the hassle of leaving Twitter to find it on Amazon's site. The more convenient and seamless the transaction process is, the more likely that you'll go through with it.
Here's Amazon's official promo video: