Upgrading from Ubuntu 11.04 "Natty Narwhal" to Ubuntu 11.10 "Oneiric Ocelot" installs Ubuntu's Unity, which changes the configuration of the window switcher that is usually bound to Alt-Tab. Instead of switching between all windows, it now switches between applications.

These are instructions on how to revert the behavior back:

In gconf-editor:

1. Disable the Super (Windows) key by editing /apps/compiz-1/plugins/unityshell/screen0/options/show_launcher and changing the value to the blank string.
2. Disable the unity application switcher (which is what handles Alt-tab by default) by switching all of the /apps/compiz-1/plugins/unityshell/screen0/options/alt_tab_ settings to Disabled
3. Add the shift plugin to /apps/compiz-1/general/screen0/options/active_plugins
4. Optionally, to switch the keyboard shortcut from Alt-Tab to <Windows Key>-Tab and have it flip through all windows instead of just the windows on the current workspace, change:
   1. /apps/compiz-1/plugins/shift/screen0/options/next_key to Disabled
   2. /apps/compiz-1/plugins/shift/screen0/options/prev_key to Disabled
   3. /apps/compiz-1/plugins/shift/screen0/options/next_all_key to <Super>Tab
   4. /apps/compiz-1/plugins/shift/screen0/options/prev_all_key to <Super><Shift>Tab