I have Ubuntu 12.10 and I want to make unity launcher to auto-hide but when it hides it doesn't appear again unless I press the start button. Should I reinstall unity through terminal? I don't have any updates and the fastest speed and sensivity didn't work.
I had the same problem. In my case it was related to the compability nvidia-current-updates (wich I installed before the upgrade to 12.10) with compiz.
I fixed it by installing the version 310.19 of the nvidia driver avaiable through this ppa (this is not the official supported version on ubuntu, but works pretty well):
In order to get this fix to work, you may have to reboot after installing the ppa.
The thing you refer to as Unity is "Launcher". And in the same window you set it to auto hide (System Settings > Appearance > Behaviour), you can set the Reveal Sensitivity to a higher value to make it show quicker when you hover.
And see if Reveal Location is set to Left side or Left corner as it defines which action triggers Launcher to show.