Launcher icons invisible, still work in 12.04
Solution 1:
Have you tried unity --reset-icons?
It's best to run this kind commands from tty1. Press Ctrl+Alt+f1, log in and then enter these commands:
unity --reset-icons
unity --reset
reboot
Solution 2:
The disappearing icons problem is described in bug #806248. You should mark the bug as affecting you.