It only works for cycling directions in the new Google Maps, the one where the map takes the entire width of the browser window, and turn-by-turn directions appear in a floating dropdown pane instead of in a collapsible sidebar. I get it in Chrome 34 and Opera 21, but not in Safari 5 (OS X 10.6). It's not as detailed as the elevation profile in RideWithGPS but is OK for imparting a flavor of how hilly a route may be.