If you're using Google Maps and are looking at a route from A to B, you can click any point on the path and drag it to anywhere on the map, and the route will update to pass through the point you selected. Example: http://farm3.staticflickr.com/2835/9667570442_4689c021f7_o.p...
The only downside is you can't search for the place to stop at, you have to find it on the map.
Until the recent UI overhaul, you could add additional stopping points, and drag to reorder them. It made solving the traveling salesman problem... I mean planning circuitous routes easier.
This is referring to all the push to use "The New Google Maps". One is not currently obligated to use it, but it's there and being pushed. He seems to be using it.
The only downside is you can't search for the place to stop at, you have to find it on the map.