Unity stopped working after zeitgeist uninstall
Solution 1:
Fixed by installing unity add-ons: unity-place-applications and unity-place-files.
I can call this a bug: uninstall zeitgeist, install zeitgeist and you lose unity application and place files add-ons. They should be independent.
Solution 2:
Run unity --reset. You will lose all of unity's settings, but at least it should start working again.