I've talked to several professionals recently who claim that usability is irrelevent.
Excuse me?
When I ask further, I learn that their definition of the practice of usability is actually limited to reviewing products for ease of use, and making suggestions to change. Certainly the folks over at Usability Must Die appear to think so.
This definition of usability is gaining momentum. Certainly "Usability Specialist" jobs are generally all about testing, although I've found that "Usablity Engineer" positions are not. Then "user experience" specialists will write things like this: (source)
The idea of usability, sometimes known as 'human factors', existed long before the web. It involves observing users engaging in tasks and mediating between design and the end users' needs - ensuring that customers can achieve the original aims of the product, whatever that product may be. Today, everybody is into usability. Usability originated in ergonomics, information design and software design, and was epitomised in the 1960s and 1970s by military displays and cockpit panels. Now it has come of age. It used to focus on product design - for example, trying to make your video remote control work properly. Today, a combination of ubiquitous computing power and the internet has made internet usability appealing to just about every business worried that it might be out of touch.
In fact, human factors and ergonomics are largely synonomous. So says The Human Factors and Ergonomics Society, so also says Wikipedia. They each involve understanding human needs and characteristics and how to apply them to the design of products, furniture, airplanes, software, or anything else. There's a good reason why schools with these programs usually have degrees available in both engineering and psychology, with possible programs in computer science, technical commuication, and design.
The breakthrough with human factors (originating with US Air Force work, WWII) and ergonomics was simple: rather than requiring the human, the user, to adjust to the man-made environment, the environment (tools, doorways, cockpits) should be designed to "fit the task to the man".
The US tends to prefer "human factors" while the rest of the world tends to prefer "ergonomics"; there is also a vague connotation that "ergonomics" refers to neck-down design issues (think ergonomic chairs or mice) whereas "human factors" gets neck-up issues (cognition, emotion, etc.).
Usability is the degree to which a product is easy to use. It is one issue, one collection of measures, within the larger user experience. Pleasure, enjoyment, and learnability are other issues. Usability is measured in "usability testing", by asking users to try out the product, and observing them. However, usability is achieved by starting with good information about the users (using research, general principles, and so forth), applying good design techniques, and checking your work at key points using various usability testing techniques.
Note the critical role of design. I thought this role was so important that I picked up a minor in design when studying human factors and ergonomics.
There are times when usability is irrelevant, such as in game play. It might make sense to require the game player to achieve a degree of skill using an obscure interface before competitive scores can be achieved. Business needs must dictate the relative importance of usability for a certain product.
The main points I hear from usability foes is that enjoyment and usefulness are ignored by usability, and that usability is all about reviewing products. This simply isn't true. What is true is that usability is one of many measures for a product or service. Foes complain that Jakob Nielsen's site is ugly and unusable. Nielsen's site certainly would be improved with some decent visual design. In fact, I imagine that the architecture of the site could remain exactly the same, and that usability would improve if good visual design techniques were applied. Enjoyment or pleasure would definitely improve.
Oh, and what is the difference between usability testing and quality assurance? In theory, nothing. In practice, I have worked with QA teams repeatedly to try to get some well-crafted standards into the QA process, but I have yet to run into an organization that enables QA testers to do anything outside of a strict script. Only standards testable without users can be incorporated into the QA process.