I was one of the original beta Mac developers, back in '83. Before the Mac was released. The idea then was to visually duplicate real world interfaces, and I gotta say they are easier for everyone, across the board, to grasp. Still, to this day, there are many people who do not use computers on an hourly basis, and they certainly do not get familiar with flat interfaces. However, the much maligned over-done interfaces are grasped immediately. Imagine that. It is because the software operates to mimic a real world item that person of many is familiar using already, without software. It is as if the entire reason for the UI is being missed by modern UI "experts" because duplicating real world objects and their innate feedback is too boring, or something. Imagine it as a stepping stone to n augmented reality where you are mimicking real world items, if you must. Real world mimicry is intuitive, and that is hands down easier. I don't need a study.