I know there are some changes in UIs and windowing systems that many people apparently consider indispensible improvements, but which I couldn't care less about. One example is the rise of compositing window managers. IIUC, a compositing window manager has to store a bitmap image of every window in RAM. But it would be fine with me if in this regard, our systems still worked like Windows XP, Mac OS 9, and X without something like Compiz, where things are drawn directly to the screen when necessary. That alone wouldn't get us back to a comfortable multitasking system in 64 MB of RAM, but it would be a start.