1) Alt-tab switcher highlights 2 big icons with the same color value. Which is my current app and which is the one I'm going to switch to? I have no idea. Takes too much brain power to process the signals.
2) Default binding of Alt to the search box thingy. Whose bright idea is this? Binding the key closest to the thumb = invitation to trigger the search box erroneously all the time, especially if you use Emacs or used to using readline shortcuts in the Terminal.
3) Where the hell do I go to configure anything? How do I rebind Alt so I can get readline keyboard shortcuts everywhere?
4) Why do I sometimes get multiple of the same app icon in the dock?
5) How do I switch to another instance of the same app? It doesn't work like Windows or the Mac, the only way I discovered was point my mouse to the tiny little arrowy markers on the left of the very subtly active app icon to trigger a Mission Control-like thingy.
6) Don't even get me started with the unavailability of Chromium on 12.10 and the Amazon search results...
If this doesn't kill Linux on the desktop (if it's not dead already), I don't know what will.