I work in a company where we have to warp the clients supplied Illustartor or PDF artwork to a gridded template (Curved shape). Sometimes clients warp the artwork for us, but use the warp effect via the Menu - Effect - Warp. Bad idea. The reason being is if you rotate the selected items, the warp effect "rewarps" the artwork, completely distorting it. A better method is to use Menu - Object - Envelope Distort - Make with Warp. Problem solved.