But this user test, while fascinating, is somewhat artificial and it's probably not helpful to exaggerate its importance.
Joe was not a clean slate, he clearly was bringing in all kinds of baggage. He was ashamed he didn't already know. He'd already experienced failure with the discount card email experience. He had someone literally looking over his shoulder and taking notes on his failure. I'd feel kind of stressed out about it too!
Furthermore, he was given a specific task (locating a restaurant) with a completely general-purpose computer interface and absolutely zero help in figuring it out. Certainly this situation does occur in real life, but is it common enough that it should drive the design of user interface?
The mall probably already has a kiosk for those users with a touchscreen UI. It would be silly to expect every user to use nothing but a touchscreen interface. Oh wait a minute...
The ones to blame for Joe's stress and frustration are us software authors. We are already treating our customers that way.