All design involves rigorous testing in the environment where it is most applicable. Design needs to be beta-tested until as many, or ideally all, of the bugs and problem areas are found and fixed. Specific and meticulous testing results in good design, and design that won't have problems in the future. Like Katherine has said many times in class about website design, the best design features shouldn't be noticeable, they become noticeable once the design is broken and technology has failed in one way or another.
This chapter of Norman goes in depth with the design of what is now the modern day keyboard. Design choices that one could say have nearly replaced the pen and pencil when we write. The keyboard layout was designed by CHarles Latham Sholes in the 1870's. Something as common as the "shift" key today took years to develop on type writers. The amount of time and energy that went into producing a valuable design was well worth it, and today there are many many keyboards in nearly every home in America.
Later on in the chapter I was most interested in Normans views of design and aesthetics. He said "If everyday design were rules by aesthetics, life might be more pleasing to the eye, but less comfortable; if ruled by usability it might become more comfortable but uglier. If cost or ease of manufacture dominated, products might not be attractive, functional, or durable." I found this very interesting, because as a good design it's the amount and balance of all of those parameters that confine ones ability. When working with a budget, or for a particular style, one must use what they are given to achieve a necessary result. There are clearly designers that sway more towards the visual side of design than usability, but thats why there those design who make ugly, but practical products.