By the 1990s, user-friendliness had become so ubiquitous in software development that even the fictional programmers in Douglas Coupland's novel Microserfs named their two pet hamsters Look and Feel. Although Coupland was confident his readers would get the joke, not all system-building companies understand the full implications of the terms.
Interface designers may be obsessed with how pretty their creations look, but it is how users feel at the end of a task that really determines how usable a device is, according to human-computer interaction (HCI) guru Donald Norman.
As professor of computer science at Northwestern University, Chicago, with a long history in computer and user interface design, Norman believes it is the system powering iTunes behind the scenes - not the iPod's circular touch-and-scroll interface - that makes it so user-friendly.
"What people miss about the iPod is that it's not about the device," he says. "Apple did a magnificent job of the entire system, from licensing the music to the iTunes website. People don't know it's an SAP website - they think SAP is horrible and complicated and don't know how to use it. They don't know what they're using with iTunes. Then Apple makes it easy to connect the iPod to your computer. It's easy to get to iTunes. There's all sorts of trade marks and digital rights management on top of that, and it's all invisible to the user."
Norman's background in psychology helps to explain his focus on users' emotional state when they interact with technology. His first degree was in engineering, but gained a doctorate in psychology and forged his early career in that field.
The combination of psychology and engineering helped him find the key to usability. "It's all about people," he says. "I find the most important thing is the emotional state of the people when they are finished."
Since branching out from psychology into HCI, Norman has written many books, as well as founding usability consultancy firm the Nielsen Norman Group with Jakob Nielsen, a Danish expert in HCI who has worked for Sun Microsystems and Bell Communications Research.
Norman praises Apple and Amazon for backing their website design and device usability with applications and infrastructure to support them and become an essential part of the user's overall emotional relationship with the device or service.
"What people care about is that they want to get their job done and feel happy when they're finished," he says. "On Amazon, when you purchase, you get a variety of emails, you have a few hours when you can cancel, it says here's where it is shipping from and when it will arrive with you. I consider that more important than 'traditional' usability."
So it is not only an organisation's ability to design applications or websites that matters, but also whether it can create the supporting infrastructure to make the whole experience useful and pleasant. This calls for breaking down departmental boundaries and allowing multidisciplinary teams to consider the user experience throughout the process, he says.
"The organisational structure of the company gets in the way. You have the design team in one corner, the engineers and programmers in another, marketing somewhere else. Then you might have manufacturing, distribution and sales channels. All these people dislike each other and fight with each other.
"The first step to getting a good product is nothing to do with the product itself - it is to do with the organisational structure of your company and the product team. Most companies recognise that is where the problem is, but changing company culture is very difficult."
After about 30 years working in HCI, little is new to Norman. "I have sense of déjà vu," he says. "Any time some comes out with a brand new idea, it is at least 10 years old. Apple brought out iPhone with touch screen, put two fingers on at once and stretch the picture, and so on. Well, we were doing that at Apple 10 years ago. Two-touch technology has been in the research lab for 15 to 20 years. It just takes a long time to get something into an effective product."
Norman's latest book, The Design of Future Things, describes the perils and promises of future smart objects, and has a cautionary tale for designers of such objects, many of which are already in use or development.
But Norman still relies on old, trusted technologies. "Today I have five computers, but my favourite device is still a notepad and pen," he says. "But I think we're close to being able to replace that with a computer."