You must have much better end users than I have. My users seem completely incapable of looking at a half finished, sort of working proof of concept and not get bogged down focusing on everything that obviously doesn't work. I definitely agree that you should talk to your end users all the time, and ideally observe them working and using your product (or your competitors product) to the extent it's possible, but I've never had much luck discussing rickety proof of concepts with them.