Mordy Golding has a post on Stiching Lines for Apparel that applies well to cartography. Say you have a cased road where you want the background image (perhaps shaded relief) to show thru. This is possible by using a combination of the Appearance Panel and Group Knockout settings. Even more advanced effects (where each side of the casing has a different styling) can be had by using pattern brushes. Read the full tutorial.