As i posted elese where, poly bushes dont allow the suspension to work in the same way as when fitted with rubber bushes. Poly bushes are only really effective in suspension that was designed to use this property. The squeek you get with poly bushes is because the suspension is rotating within the bush, rather than the bush deforming within its elastic limit.
You shouldnt grease bushes. If you do, they arnt doing what they should be. If they are rubber bushes, you havnt fitted the correctly.