Disable default Gnome Shell Super Key Mapping
Solution 1:
I found how to do this here:
Start gconf-editor and set /apps/mutter/general/overlay_key to empty string, then restart gnome-shell.
From gnome-shell 3.4 onwards, use:
gsettings set org.gnome.mutter overlay-key ''
Solution 2:
The way I got round this is in keyboard preferences to set the left windows key to be the meta key and left alt key to be alt.
This means that your left alt key is no longer a meta key - so if you use emacs, you'll need to either have to get used to that change rebind all your Meta keybinds to work on Alt instead.