Fundamentally, ui has to be a consequence of function - there's a pragmatic reality to how a thing is used that informs the limits of the representation of cont

Fundamentally, ui has to be a consequence of function - there's a pragmatic reality to how a thing is used that informs the limits of the representation of controls. In a visual context, it's less about skeumorphic analogs and more about how the brain maps those controls to things we already know. This is muscle memory and plasticity in action - the relative locations, stateful appearance, and behavior of controls gets mapped in our brains in the same way as taxi drivers learning the routes in a city, a violinist learning fingerings, or a child learning the alphabet. "Muscle memory" is required to establish foundations of more complex behaviors. Once you've built a user interface, you should not ever touch elements upon which the users have built those muscle memory mappings. Yo Yo Ma would be as lost as a child if you told him he had to play the bassoon instead of cello. After a couple years of practice, some of the higher level artistry could be brought to bear on the new instrument, but it's the low level fundamentals that matter. Firefox screwed with fundamentals, and their market share is evidence of why that shouldn't be done. Windows keeps pushing down that path as well, mistaking their current dominance in desktop as something absolute.