This is my first GNOME 3 shell extension. I created this because I saw no way to disable the huge popup displayed dead center of the screen when switching between workspaces, other than editing /usr/share/gnome-shell/js/ui/workspaceSwitcherPopup.js and setting the value of DISPLAY_TIMEOUT to zero.
Create a folder in ~/.local/share/gnome-shell/extensions called disable-workspace-switcher-popup@github.com and move extension.js and metadata.json into that folder. Restart the gnome-shell:
# mkdir -p ~/.local/share/gnome-shell/extensions 2>/dev/null
# git clone git://github.com/windsorschmidt/disable-workspace-switcher-popup \
~/.local/share/gnome-shell/extensions/disable-workspace-switcher-popup@github.com
Alt-F2 and "r" ENTER
For Gnome Shell 3.2 you also need to turn the extension on. The easiest way to do that is to install gnome-tweak-tool and go to Shell Extensions settings screen and turn it on (the switch-"thing" must have "I" on it).
Based on the disable window animations extension by Lukas Zapletal