It still amazes me that in the 20-plus years since the commercialization of the Internet, some companies still don’t get the fundamentals of how it works: That the more user-friendly a website is, the more profitable it will be. I mean, the Internet (and now the mobile app world) is littered with the presence of companies that threw a lot of money into having one. But in their rush to build more features, flashy designs and graphically inviting pages, they have often lost site of the key ingredient: basic usability.

User-interface design, or UI, is the art of simplifying complexity into meaningful user experiences. It’s an increasingly important competitive advantage for companies, as consumers seek sites, apps and products that offer as much intuitiveness as they do function. But the reality is that many still have no idea that the key to success lies in the user experience, providing the consumer with the information they want right when they want it.

Studies have validated the importance of good UI design. A 2009 Best Practices in User Experience study by Forrester Research (read the study here) finds that companies who provide a superior experience have more customers who are willing to consider them for another purchase (14.4 percent), fewer customers who are likely to do business with a competitor (15.8 percent), and more customers who are likely to recommend their products (16.6 percent). Enough said.

But if you’re still not convinced, think back to 2006, when Microsoft introduced Zune, a portable MP3 player that, despite being feature-rich, failed to compete with the iPod due in part to a more complex interface. The simplicity of Apple’s design won them the mobile media market – and Microsoft is still trying to catch up. More recently, a bad design and confusing user interface could be the reason more people haven’t adopted Google Plus (read more about that here).  Admittedly these are large-scale examples, but I can think of many more experiences I’ve had lately with bad UI design – online banking to name one, ING .

In short, I can’t stress enough the importance of a good, smart user interface: It can quite literally be the difference between product acceptance and rejection in today’s commoditized marketplace. If the customer feels that your website, app or product is not easy to learn, not easy to use or too cumbersome, your otherwise-excellent idea could be destined to fail before the customer has a chance to discover it.

I constantly find myself studying good user interface design to find out what makes it work so well, and I’m interested in your thoughts and experiences with good (or bad) UI design.