Now what? The secret sauce is tiling. [facklere] used KMZfactory, a free map editor for Garmin maps that goes the extra mile to split the tiles for you, keeping them under the 1MP limit.
The Nuvi vehicle downloads are free from a non-Garmin-affiliated third party, while most of the TomTom voices cost extra. Will this sort of thing have us trading in our Droid? Not a chance.