Amazon has entered into a partnership with Twitter whereby Twitter users can link their accounts to an Amazon account, and add items to the shopping cart by responding to any tweet with an Amazon product link that has the hashtag #AmazonCart.
In order to take advantage of the service, customers have to connect their Amazon account to their Twitter account, which they can do via Amazon.com/AmazonCart.
Customers never leave the Twitter feed, and the product is waiting for them when they head over to Amazon. However, the tweet only adds the item to your cart. The shopper still needs to go to Amazon later to check out and pay for the product.