Conceptual Models

1. "...Clues to how things work come from their visible structure-in particular from affordances, contstraints, and mappings. Consider a pair of scissors: even if you have never seen or used them before, you can see that the number of possible actions is limited. The holes are clearly there to put something into, and the only logical things that will fit are fingers. The holes are affordances: they allow the fingers to be inserted. The sizes of the holes provide constraints to limit the possible fingers: the big hole suggests several fingers, the small hole only one. The mapping between holes and fingers-the set of possible operations-is suggested and constrained by the holes. Moreover, the operation is not sensitive to finger placement: if you use the wrong fingers, the scissors still work. You can figure the scissors out because their operating parts are visible and the implications clear. The conceptual model is made obvious, and there is effective use of affordances and constraints."
I found the idea of conceptual models quite fascinating. The author suggests that when a user uses a product, they must first design in their own head an idea of exactly how they will interact and how the product will respond to action. What is necessary to operate this product and what will it do? A conceptual model answers these questions. Conceptual models are very easy to construct (in our minds) for some products, and I believe that is an affordance in itself.
Norman goes on to describe products that do not afford conceptual models well, such as his refrigerator. Without clear physical mapping or affordances, products do not lend themselves to usability.

2. Norman's book spans time by describing design issues that are themselves timeless. The resolution of these issues is just as applicable to products today as they were in 1988. The human race has not, in fact, become more skilled at using difficult products. New merchandise still needs to be carefully mapped and conceptualized before a user can utilize it. Designers' ability to create usable products depends on their skill at implementing affordances and constraints.

3. My checklist would include a few basic ideas: the product must be obviously functional (easily conceptualized), must be as simple as can be reasonably expected, and must perform to the user's satisfaction. The last factor mentioned, "satisfaction," relates most to comfort and style; or, the product should be convenient and reasonably fashionable.