I have been testing Ubuntu Gutsy and after various updates I would lose my Compiz Cube. I would be left with only two workspaces (Desktops). The easiest way to fix this problem is by doing the following.
Alt+F2
type 'gconf-editor' into text box
then, click on 'Run' button
apps/compiz/general/screen0/options
set 'hsize' value change to 4
close 'Configuration Editor'
