This is a great introduction to mainstream ideas surrounding utility. Hopefully, I am not out of line if I pushback against the mainstream a little bit....

The biggest problem with "utility" is the simple fact that there are no utils in the world to be counted or measured. I see three potential responses to this problem:

1. The Neoclassical approach is to say that utility is simply a conceptual framework that they (the economists) themselves impose upon acting individuals. As such, people act "as if" they were maximizing utility when, in point of fact, there is no such thing to be maximized.

2. The Austrian approach insists that Neoclassical efforts to impose a relatively constant framework upon human action is forelorn, since individual values change far too fast for us ever to gather enough behavioral data to ever build a robust utility function - and even if we did gather enough data, such a function would quickly expire as the individual's preferences shift again. The Austrian solution, by contrast, is to make utility an utterly subjective value that only resides "inside" each individual actor's mind, totally beyond the direct observation of any "outside" observer.

3. The Pragmatist approach totally rejects the "container" metaphor at the heart of the Austrian approach, while at the same time remaining aloof from the Neoclassicals efforts to cram changing, qualitative actions into a static, quantiative model. Instead, "utility" and "value" are words or signals by which we coordinate, rationalize and even justify our actions to each other. These words to not "correspond" to any object at all - whether it be out in the objective world or "inside" the subjective container of the mind. Instead, all such talk is like a quarterback calling an audible during a football game in order to coordinate the teams future actions.

No doubt, other approaches could also be listed, but I fear that this little addendum has already exceeded the word limit that etiquette demands. :)