Re: Dear Matias,
The definition of intuitive might vary from one person to the next.
Not everyone considers touch interfaces to be intuitive: touch interfaces often require the user to memorise arbitrary and unnatural gestures to accomplish basic tasks. For example, one big argument in favour of a mouse interface is that it enables "discoverability": users can see all the main objects on the screen and can even see pop-up context help as they roll the mouse pointer over each object, so it becomes possible to explore the interface and discover new features. Discoverability favours recognition over recall: human memory is much better at the former than the latter... it's much easier to recognise an icon or a named menu option previously seen than to drag it from the depths of the brain. Also, the longer a familiar interface remains the same, the more entrenched the mental schema for replaying known actions becomes. A new interface that is "almost-but-not-quite-the-same-as-before" can be very disorientating (e.g. "Where's the start button?" etc.). Knowing a bit about how the human brain works can help to design better user interfaces for the majority of users.
Of course technology moves on... it's not convenient to carry a mouse around with our phones and also people will prefer cleaner less cluttered interfaces on devices with smaller screens. Some of the specific challenges we face will vary as the display and input technologies evolve, but designers must not forget that there's a human using the device and the fundamental human "hardware" has not changed. In my degree many years ago, we learned about researchers like George Miller and Ben Shneiderman: they taught us a great deal about human memory and cognition which can be used to inform interface design. Psychologists could definitely teach us a few things about how to design systems for regular people and for my money Shneiderman's 8 golden rules are just as valid today. So I agree with the point that engineers are not always the best people to design a UI, as we often lack these insights.
Having said all of that, I'm a bit suspicious of the current fad around interface design. I believe good design is important and it's great to see it becoming more of a discipline. At the same time, I've seen some very fiddly and unnatural professionally-designed interfaces which are difficult to use and violate many of the good human-based design principles I learned back in the day. And sadly a few people who call themselves designers are too arrogant to listen to criticism from actual humans (constructive or otherwise).
Innovation is great, but everyone involved in designing systems should remember the humans who have to use the end product and listen to their feedback. If the majority of users hate something about a UI even after having lots of time to adjust then their rejection of that feature should be heeded. That doesn't mean never changing the UI, but it does mean careful thought and research before doing so.