If you are running compiz (desktop effects) you will only see one desktop on the bottom right, to add more install the advanced desktop settings package "compizconfig-settings-manager" by opening a terminal and typing
Code:
sudo aptitude install compizconfig-settings-manager
Now you can access it from your System-->Preferences menu
Here you can modify all the plugins to your hearts content, Click on the General options and select the desktop size tab, here you can add and remove desktops for the switcher.
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