Frankly speaking,cube has a special space in my heart.This is the desktop effect which i used to lure people from windows to linux;and i am sure i am not alone in this.Lots of other people has done the same thing.
The problem was due to unity's dependence on the wall plug-in directly.Now they have changed this to 'laredesktop' only following a bug report.Now to be used properly,compiz needs to be provided with a profile with cube already activated.Just follow the following guideline to use cube and reverse it to activate wall again.
Go to “Preferences”, at the bottom on the left-hand-side. Then deselect “Automatic plugin sorting”. You will get a warning message, select “Yes”As natty is still a beta,it might cause some crashes.So do not use this,if you want a stable system.Thank you
Now find the plugins “cube” and “rotate” in the left hand list of disabled plugins. Select them, individually and click on the right arrow to enable them.
Next find the plugin “wall” in the right hand list of enabled plugins. Select it and click on the left arrow to disable it.
Now have have set the plugins, reselect the “Automatic plugin sorting” checkbox and go back to the main page.
Click on the “General Settings” icon, which is usually near the top of the page. When this has loaded, go to the “Desktop Size” tab and change “Vertical Virtual Size” to 2 and “Horizontal Virtual Size” to 2 (the last part is not absolutely needed;though i use a 2by2 grid).