I have a try monitor setup with using the proprietary ATI drivers:
This works pretty well with metacity, with the exception of some maximize strangeness. On monitors 3 and 2 it works as expected. However, if maximize a window while it is with monitor 1 it maximizes on monitor 3. So I figured I would try Compiz.
When I start compiz with
compiz --replace monitor 1 (forgive the backward numbering) goes black. The monitor does not lose power. I can still see the cursor if I move my mouse over to it, however compiz will not let me drag any windows to monitor 1.
I tried to set my outputs in ComizConfig Settings Manager but it doesn't seem to make a difference: