I've used Postmates a couple of times at work when I've been too busy to actually go out to lunch. I can also see using them in a few other situations. I've been very happy with the service, but I'm not sure the market is as big as people are hoping.

But interestingly, I see this as a huge win for people that may be home-bound due to age or injury. Specialty services that cater to this demographic are expensive and not nearly as responsive.