According to : http://www.revouninstaller.com/revo_uninstaller_uninstall_features.html
"Revo Uninstaller Pro scans for leftovers with even more advanced algorithms that are so precise, fast and very effective in search for leftovers of Windows Services, Drivers, File associations, Shell Extensions, COM components, Windows Installer components, program settings and more!"
So their uninstaller should uninstall things completely.
So after installing this you should be able to uninstall programs completely with it, but if you meant left overs of older uninstalled programs i think "what's in the past is past" it cant probably clean up after a previous uninstall if that is what you mean :-)
Hope this helps