My unity crashed during the update from 11.10 to 12.04, and after waiting a long time i was forced to restart the computer. when it came up, things were in a sorry state, i got to the terminal and ran sudo dpkg --configure -a and it seemed the update resumed. after a reboot, everything seemed ok, except when going to the applications launcher, there a search bar for applications, but no filter results button, and searching for apps yields no results. there are also error messages that pop up about the unity application lens having a serious issue.
The answer got from here
The disadvantage: you need to reset your unity-related shortcuts
Some users found that it was not necessary to reset unity with its associated loss in shortcuts. A restart of X was sufficient.
i may have found the answer:
I copy/paste the solution given:
"Here's a summary, for those experiencing the same problem. In short, we're not sure action originally led to this problem, but somehow at least two packages were inadvertently uninstalled: unity-place-applications and unity-place-files. The removal of these packages seems to cause Unity to seemingly forget what applications were installed (and probably what files as well). Zeitgeist seems to still work, and remembers newly installed packages.
To fix the problem, simply reinstall the unity-place-applications and unity-place-files packages, then restart just to be safe."