Google Maps now allows you to drag and drop points of your route to override the default and redraw the route from new waypoints. While planning our wedding and putting a map (that my graphic designer husband created on his own in Illustrator based on directions we got from Google Maps) I would have LOVED this feature about 7 months ago! There is a video demo of the feature here:
I haven't had a chance to play with this yet, but I encourage you to go have a look. It's especially good, most likely, for people who live in or near big cities where the default directions aren't bad but don't 'know' about local traffic patterns and can often send you into or across toll roads to go half a mile. Try to send someone from Fort Lee, NJ to Hoboken, NJ and not have your directions send you across the George Washington Bridge and then back through the Lincoln Tunnel. It's happened to me in the past, and I can't tell you what a bad idea that route would be.