In Santa Monica and Culver City in Los Angeles market I usually see 2-3 amazon fresh trucks on my daily commute to and from work. It's rare anymore that I don't see one. I've also seen several companies that are using them to stock the company fridge with things like milk. It looks like it's taking off fairly well anecdotally. I don't know if there's been any numbers published though. The biggest hurdle I've seen with it is that the site for it is woefully underpolished. It's not buggy but it tends to be slow, and a little obtuse to browse on at times. If you have something specific in mind it's really easy to find it, but if you wanted to say just look at the different types of potato chips they have, it can get a little unwieldy at times.