the bug affects Nvidia users...
https://bugs.launchpad.net/ubuntu/+s...z/+bug/1166765

temp fix is open a terminal <ctrl> <alt> <f1> and execute the following:

$ gsettings reset org.compiz.core:/org/compiz/profiles/unity/plugins/core/ active-plugins
$ shutdown -r now

fixes it but maybe not permanently yet so keep this note handy.