Today I was trying to resolve a longstanding annoyance, the fact that changes I make in CompizConfig Settings Manager do not persist after a reboot. Googling around, I saw that this appears to be a current bug, but one person claimed to have fixed the issue by going into CCSM's Preferences, then changing "GSettings Configuration Backend" to "Flat-file Configuration Backend".
That seemed like a harmless enough thing to try, so I tried it. Immediately after selecting the flat-file option, Unity died. I was left with only the unadorned windows of programs I was running at the time. I tried rebooting, but came back to a desktop with Unity still dead. Fortunately one of my desktop icons is for my web browser, so I was able to start searching for a fix.
After some fruitless twiddling in /etc/compizconfig, I was able to launch CCSM from the command line and reverted the option that had caused all the trouble, but Unity stayed dead. Eventually I read that I needed to enable the Ubuntu Unity Plug-in. I did so (not that I'd ever disabled it), and was asked if I wanted to enable various other plug-ins, to which I naturally agreed. Another reboot later, Unity was back! Sort of. The launcher and desktop title bar (or whatever it's called) were back, but now whenever I start an application, the window appears in the upper-left corner of the screen, partially obscured by the launcher and title bar, and it doesn't sport any of the usual window manager dressing that would enable me to move it around, resize it, etc.
And here I'm stuck. Any help getting the rest of the way to a working desktop would be much appreciated.
(Unity does seem awfully fragile. Last week I tried to unmount my iPhone by right-clicking on its launcher icon and choosing "Unmount," and that killed Unity too somehow. In that case, however, a reboot brought it back.)