Top left: nothing
Top right: Dashboard
Bottom left: Screensaver
Bottom right: nothing
After the few months I've had my Mac, I still really haven't found any use for Expose other than just using hot corners (and honestly I wouldn't be using those except that's the easiest way to invoke the screensaver (where it was just a keystroke in windows.)
Rather than using expose, I have my scroll wheel button set to hit F8 to pull me out to a full view of all my spaces, then I just click into the one I want (I actually barely use the key combo to switch around spaces anymore.)
-Bryan