I was watching an interview of Alvin Toffler (the author of Revolutionary Wealth) and he said something that really struck me. His example of the problem with measuring national GDP was that when Microsoft spends millions creating a new version of Windows that is only marginally better than the old one, the measure of GDP goes up based on the money spent on it. But when thousands of programmers contribute to the development of Linux for free and thousands of companies download and use the software, again for free, there is no recognized effect on GDP.
I wondered about Human Factors in this same way. For the past few years we have been struggling to make the business case for Human Factors by proving that it increases sales, etc. But are there other effects that we are missing? I think that a usable product, even if it doesn't make me more productive at work, still makes me happier, and maybe more productive overall because of my mood. Or maybe just the happiness should be measured.