After upgrading to 12.04 the keyboard shortcut of the windows manager (Metacity) such as my custom Alt+1, Alt+2 for desktop switching but also the default Alt+F10 for maximizing window stopped working in Gnome shell. Anyone knows what might be the cause and/or remedy?
Gnome-Shell uses not Metacity Window Manager, but new Window Manager - Mutter, which uses new configuration system - dconf, while old GNOME and Ubuntu Unity interface uses old configuration system - gconf. Because of this "System Settings" -> Keyboard -> Shortcuts doesn't work on Ubuntu with GNOME3 shell :(
See Ubuntu bug #965921 for more info and workarounds.
Some useful info also can be found here: blog.sudobits.com/2011/10/12/top-10-gnome-shell-keyboard-shortcuts/
in ubuntu 12.04 gnome-shell keybindings were modified so that WindowsKey and CursorKeys now control Window Maximization and Left-/Right-Side Splitting, while moving between Activities (aka Desktops) is now controlled by Ctrl-Alt and the Up/Down Keys.
To get back to much more useful behaviour, install dconf-tools and execute these dconf commands from the shell:
You will get:
Thus your Ctrl and Alt Keys are once again freed up for your applications, like they should be, and only the WindowsKey is used for Windows/Desktop management.