I would say that in the long term/big picture we have figured out a pretty standard UI for computers. In the 1980s you probably had to read a pretty hefty book

I would say that in the long term/big picture we have figured out a pretty standard UI for computers. In the 1980s you probably had to read a pretty hefty book for any given model of computer to be useful. Now, we can sit down in front of just about any computer and trust that the Mouse and Keyboard will exist, and act like we expect (i.e. the left button on the mouse is for selecting, there are arrows on the keyboard which can control a cursor, etc), and that the GUI software will be substantially similar regardless of manufacturer (windowed programs, a bar of some sort on the lower edge of the screen for controlling the OS, a bar at the top of the screen for controlling the active window, etc.) The parts of the UI toolkits that change are the least consequential. Round or square corners, buttons, skeumorphism, etc...