I’ve recently installed Ubuntu 12.04 Prestige Pangolin (I use Gnome Classic), and immediately noticed that the alt+tab shortcut wasn’t working. I tried fixing it within Applications>Systems Tools>System Settings, but that did not work. I have compiz Config Manager already install so I figured I could use that version instead (it looks nicer anyway).
Finally, I’ve found this solution on a forum, by installing Compiz Config Settings Manager: 1. Go then to Applications>System Tools>Preferences>Compiz Config Manager 2. Scroll down to the bottom of the window and where it says *Windows Management*, click on either Application Switcher (dynamic) or Static Application Switcher, depending on which you prefer. If you need to install Compiz Config Manager: 1. Click Alt+Ctrl+T, to open the Terminal 2. Type this: `sudo apt-get install compizconfig-settings-manager`, 3. Or search for **compizconfig-settings-manager** in the Software Center and install from there.