Robotically offering me a box seems significantly easier than robotically driving a freaking van.

Right, now we're talking about stuff that's a hundred years away (yeah I know Google car ...)

What is still left to be done? Google has extremely detailed mapping and the self driving car works well in real traffic. (One advantage a car has over planes is that if things go horribly wrong it can just stop.) http://en.wikipedia.org/wiki/Google_driverless_car

There aren't any technical unknowns left. Obviously the algorithms will continue to be tweaked and improved. Importantly it can operate in the existing environment - there is no need for every car to switch to driverless at once.

Amazon already has "Amazon lockers" scattered across Manhattan where you can go pick up your packages from a kiosk inside a grocery store / drug store. You enter a pick-up code on the touchscreen, and a specified locker opens up with your goods inside it. It's easy to see how similar tech could be adapted for use inside a robovan.

Any particular location you have seen this in NYC? Haven't seen it yet

I've personally only used the one at the Gristedes in Sheridan Square, but based on their locator (http://www.amazon.com/gp/css/account/address/view.html/ref=l...) it looks like they have a good 15-16 in Manhattan and 3-4 in Queens/Brooklyn.