One of my "favorite" paradigmatic UI changes (Mac): the Finder and Open/Save dialog sidebar. Up to and including Snow Leopard, these would include custom icons, once the flagship feature of user customization and personalization. However, this also served productivity, just assign a simple colored bubble icon to any of your current project folders and a few decent, but recognizable ones to the major entry points into your file structure, and these were easily recognized and located in any file list at a glance, without even reading a single character.
Then, Apple decided that this may endanger their precious industrial design. Finder icons, especially those for folders, are to be clean and uniform – and to be exclusively chosen and delivered by Apple. (Also, color must not serve a purpose and isn't allowed to transport any information.) Icons are not for everyone, quot licet Iovi non licet bovi. Now, it's all about reading, or, if you maintain a really clean and short sidebar, about position. Still, every time a Finder window or file dialog is accessed, some precious seconds and some maybe even more precious focus is lost. However, these are apparently not that precious as Apple's pristine looks. – OK, Apple, now I know, where I rank in your esteem. Thanks for letting me know.