I walked the Le Puy route from Le Puy to Cahors in Sept 2010 and from Cahors to SJPP in Sept 2011. The GR 65 is very well-marked, including suburban and urban areas. Marks are often on the downspouts , building corners, and the backsides of highway signs.
Usually at intersections where the route makes a turn, you get a "turn coming up" mark beforehand, and the "wrong way" marks on the incorrect exits from the junction. Waymarks come along fairly frequently, so if you have not seen one for a while, and you don't see other walkers, it is time to backtrack a little bit.
However, you must be alert! Pay attention to your surroundings so that you are aware of when you have somehow got yourself turned around and walking the wrong way. The schematic maps in MMD are sufficient. Also be very careful when crossing other GR routes, as all GR routes are marked in the identical fashion with red-and-white marks, whether going or coming.
I found the most difficult part was leaving the marked GR to find the gite for the night, and then picking up the GR marks again in the morning. It is good practice to scout the morning's route before you turn in for the night, and ask your host for advice if you have any questions at all.