>To me these are all "efficiency" measures. And hence, my explorations >of what other measures could be relevant as well. thanks~
When talking to business people I like to use a simple vertical scale with a centered horizontal line as a visual reference. I usually call that line, for lack of a better term, "sea level".
Below sea level we are primarily concerned with usability issues. Basically - how do we avoid getting in the user's way? How do we not send them down a path of failure? And, how do we discover and correct mistakes and problems? This has long been the space of cognitive study, HCI and HF. Residing soley in this space the designer is in essence playing to "not lose" (please pardon the sports metaphor). Most of this is in some way measurable. It is comfortable. And, it is a very scientific like endeavor.
Above this space is a somewhat uncharted area. This is what is really exciting. It is the space where we take chances, risk being completely wrong and our entire effort is focused on enhancing the experience. We are "playing to win". This, is not so quantifiable.
The reason that we have developed a methodologies and tools for inline, in process, low fidelity interaction research is to allow our designers to take more risks. This is where the fun, the innovation, and largest benefits reside. Granted it is very risky and we often fail... but we don't risk complex or extraordinarily refined prototypes here. We play.