Compiz question

[Bart Silverstrim]

I have two systems running 7.10.

The one system has a feature enabled that I don't know how I did it...I 
move the pointer into the upper left corner of my four-desktop cube, and 
the display "zooms out" to show all four desktops side by side, where I 
can move windows among workspaces and see real-time content of the 
windows.  Double clicking on a desktop or application from that view 
zooms into that workspace to fill the screen again.

The other system I don't have this available by default.

I don't see in gl-desktop where this gets enabled.  According to that, 
there's nothing assigned to the upper left corner of the system that 
it's doing this with.

Any clues??