Comment 4 for bug 998285

Urustu, do you mean stop using Unity and use Gnome-shell?

Also, I've happened upon a workaround while still using Unity. Install ccsm, then deselect Desktop > Ubuntu Unity Plugin > Switcher > Automatically grid windows on timer in switcher. You might need to run "$ unity --replace", but I can select or deselect this setting and the alt-tab behaviour changes accordingly. It's a bit funny that this setting should have this side-effect, as it's not directly related.

(Turning on this setting does the following. When holding onto alt-tab, if you hover over an application icon with multiple windows open, after a short time the window thumbnails are exposed. If this setting is off, then alt-tab only shows the application icon.)