Today after a reboot, Ubuntu blurs text (well, anything that is rendered on screen) whenever focus changes or on any interactions with the desktop.
Normal good look:
Note how the text, folders and the plus signs left of the folders are somewhat blurred. In this case, the normal state is after opening the window. Blur happens on lost focus, and gets normal again whenever something is redrawn
This applies to anything that is drawn. Even in 3d games, text and thin lines flicker between normal and blurred intermittently, or whenever desktop interaction happens.
I have ruled out anything to do with font smoothing, this seems to be opengl-related.
Does not occur if I switch to Unity 2D or Gnome, but then again, that's not what I want to use.
This just in: As it happened, the issue fixed itself while typing this question, after Compiz crashed and restarted itself while trying to provoke the issue. Strange, seeing how the issue survived several reboots.