I found here the exact question i want to submit, that is :
"I set /apps/metacity/general/num_workspaces to 1 using gconf-editor but when I do +s it still shows my workspace in the top left corner with the rest of the screen black. Shouldn't it just zoom out and show all of my running apps expose-style for that single workspace? I want to use -s as an expose-style app switcher. I've never been a big workspaces fan, so I just want the one."
Thank you !