A common claim at the time was that Exposé was a copy of those same virtual desktop programs, or even that it was a copy of Alt-Tab.
That said, even the writer of Virtue Desktops doesn't seem the think that Apple Spaces is a mere copycat, but rather that it "addresses many of the current usability issues that seem inherent to existing desktop management tools". Link.
Expose is s simple action that allows you to easily look at all the programs that you are running. Hit F9 and every program shrinks so you can see it all at once. Hit F10 and every window you have open in a single program (like multiple windows in Safari) will be the only things view. F11 clears out all your windows so you can access your desktop really quick. It's neat and simple. And if you hold shift when you push the buttons, it goes in slow motion.
you can also tie it up with your hot corners to access those features from the corner of your screen.. I have screensaver top left, all windows top right, dashboard bottom left and reveal desktop bottom right.. It is so useful.. i would recommend giving it a go