Shneiderman presents an orthodox view of user interface design strongly influenced by experimental psychology. This is a good place to start, but it only goes so far. The first chapter was boring to me, and I suggest you just skim most of it. The next to last paragraph of section 1.5.1 (page 20) does give a good example of how the social can impact even ergonomics. The remarks about intelligence on page 21 and video games for women on page 22 are provocative, but without enough detail to mean very much. The emphasis on diversity is nice, and there are lots of references (maybe too many :-).
There are some interesting things in chapter 2. The critical remarks about reductionist theories at the beginning of section 2.2.5 are good; in my experience low level measurements and theories aren't usually very useful. Cliches like "Recognize diversity" and "Know thy user" are worth repeating. The list of needs for 3 classes of user on pages 68-69 is useful, the list of advantages and disadvantages of styles of interaction (pages 71-74) is really useful, and the "Eight Golden Rules" (pages 74-75) are good reminders. However, such lists are not as useful as you might hope, because they are far easier to apply with hindsight than at design time! The 5 points on page 80 are again good reminders, but as Shneiderman points out, they are too vague; on the other hand the bullets on pages 80-81 are too project-specific (and the last bullet is probably more radical than Shneiderman realizes). The discussion of agents in section 2.9 is very interesting, emphasizing the role of responsibility; later we should read Lanier's piece. I'd like to emphasize a sentence on page 89: "Extensive testing and iterative refinement are necessary parts of every development project." It's amazing how often engineers think they can get things right the first time - and then end up wasting a lot of time as a result! I think the most important lesson from this chapter is that good design is much too difficult to be subsumed by any simple guidelines or theories; it is at least as much an art as a science.
I was surprised to learn that most class members did not know much about what psychologists really do, so I tried to give some background to help understand the first part of chapter 2; here is a summary. In sections 2.2 and 2.3, Shneiderman is talking (in part) about experimental cognitive psychology. Cognitive psychologists make theories of thinking, and especially they want to know what kinds of theory work well. Only after a theory has been validated for a particular class of applications can it be used to make predictions that are relevant to real design issues. So experimental psychologists devise experiments to test theories. To run a test, you need something very specific, not just general features of a high level theory; however, the point of the experiment is usually to determine whether a particular kind of theory works for a certain class of experiment. As a rule, industrial psychologists are more concerned with actual applications, and academic psychologists are more concerned with the theories themselves.
We had a good discussion of what "user participation" might actually entail, noting that it could be difficult, frustrating and even misleading, but that it was probably essential. In particular, we discussed the use of various prototyping techniques to get user feedback very early in the design or even requirements phase of a project. We noted that this was one place where social issues can enter in a very significant way. One particular point was that asking users why they do something often does not work: much of user knowledge is tacit rather than explicit; moreover, users often have not previously thought about issues that designers want to raise, and even if they have, they may have a biased point of view.
I strongly recommend re-reading section 2.2.5 several times; it is a good summary of some very important points, but it is also very compact and rather obscure.