It's been an issue for quite some time to set the number of different desktops (or workspaces if you like) in the new Ubuntu Natty Narwhal (using unity).
Some guys figured out a way to overcome it by using the compiz-config(CCSM). For some reason it seems that the CCSM doesn't really work for me. I change the number of desktops, and the expo but it won't work.