2) I guess I don't like the concept that posting to a social network gives one more punch than not doing so. I don't have an aversion to twitter or facebook etc, I use them all the time. What I don't like seeing is auto-generated posts from my friends flooding my news feed. I'll admit I have no better solution than you've devised, and I completely understand the decision. Some others might have more of a backlash against it though. You may have seen some vitrol on here whenever someone sees a "login with Facebook" link on a startup's page.
3) That makes sense. It's kind of disappointing from a technical limitation standpoint, though. The reason I called it out as possibly being a barrier to entry is because 4.0+ still isn't terribly common. While iOS is very common, I was sad to see Windows Phone, Blackberry, and other touchscreen smartphone platforms not included. Like I mentioned in my footnotes, we're used to it, but I still like to call it out.
1) Not a problem. My criticisms were posted just because I like to give positive and negatives to interesting startups I see and like. There are some things people might not see from the inside out. This is a very non-traditional checkout method, and I could see non-traditional businesses loving it. Good to know you're willing to work with them to meet their needs. When I wrote that I was thinking more along the lines of alternative use-cases other than POS terminals. The ideas you have are just the beginning of where this technology can go.