I personally don't see any need for this in my life right now, though I do buy a lot on Amazon.
For marketers, this could be a huge deal.
Even people like small authors could do great with this: they can have a smooth transition from talking about their book with people online to having them buy it without relying on people's keeping their short term memory together so they remember to pick up the book. Authors sell books on their book tours because people don't have a chance to forget to pick up a copy.
If you find it annoying, you can just either not follow the Amazon accounts or block them. This is a nifty little thing, and it'd be a shame if it gets screwed up.