I think it was all a publicity stunt. Big Amazon story on the evening before CyberMonday? Possibly coincidence, but I doubt it.
Along with all that's been said already here are the technical/logistical challanges that will keep this from happening:
1) Battery Power
Amazon says they’re shooting for 30 minute deliveries.
Jeff Bezos said they will deliver to within 10 miles of an Amazon Fulfillment Center. That would mean they would have to go at least 20mph. They will be carrying up to 5lbs (projected upper limit of package size) Carrying that much weight at that speed for up to an hour is going to require some heavy batteries.which will add more weight and becomes a vicious circle.
The could use gas power, but they are noisy and annoying and will get a lot of complaints really quickly which will lead to city ordinances (at the least) state/federal laws at the worst.
2) Weather
The propsed drone is an octocopters. They can do pretty well in a decent wind. But sending them out in rain or snow would be bad. They can add wet weather protection but that would add more weight and may not be worth it. Will Amazon risk sending orders out in storms? They could loose both the drone and the shipments that money would add up quickly. No flights during bad weather? Customers would be upset.
3) Theft
This would be one of the biggest issues I think. What is to stop anyone from stealing the shipment? Or waiting and throwing a blanket over the drone and stealing the whole thing? Identity theft would be even easier with these. Steal someones credit card order to any address, wait, grab item and run.
They could put video cameras on it, but now there are privacy issues. Some cities have already passed legislation against drones with cameras (Invalid Link Removed for example)
4) Navigation
Taking off and heading for a coordinate is easy. There are hobbyist that make them already (check youtube). However, doorstep delivery in a residential (or urban) area, just GPS won’t be enough to keep the drone, and everyone in the surrounding area, safe. To reliably land on a customer’s doorstep Amazon can use cameras to make sure they aren’t landing on a tree or person but that will raise the same concerns listed above. Where will they land for customers that live in apartment complexes, high-rises or dormitories? Will they send out teams to “pinpoint” ideal landing locations? Google has already been in trouble for privacy issue with this in the past. They can get some leeway with the "streetview" because they are on public property. They would have to get permission from eveyone to use their private property for this.
5) Safety
The instant one of these falls out of the sky and lands on or near someone, Lawsuits galore for Amazon. Or even worse, on breaks fall and lands on a car in the middle of the highway. The drone itself doesn't even need to cause a lot of damage, the surprise of being hit by one of these falling on you while driving highway speed can cause a collision.
One death, Amazon will be bankrupt.
6) The FAA
Amazon has no control over this. Amazon says the 2015 goal is the earliest possible arrival of Drone-related FAA Rules and Regulations. That is not a firm deadline. That's when the FAA said they MIGHT have something out. It maybe 5 years after that.
I can't believe someone as smart as the folks at Amazon and with the resources at they have wouldn't have thought of these issues making it nearly impossible. In fact I'm sure they have thought about it. But you get a nice puff piece on a national show the day before a big online sales day and get a lot of people talking about your company..
You can't buy that kind of publicity..