Shortbus...
Well.. noniGPSplot isn't "tied" into Google Maps.. but the waypoint abilities are outstanding.
GPSplot allows for "Moving Maps".. fancy wording for a big picture you have saved of a map... You can import this pic and the map will move when your location moves... just like google maps.
It sounds like you want to use your data connection when available... but if it craps out.. then you want a cached map to work with...
Perhaps this could help....
http://www.metacafe.com/watch/107391...ve_large_maps/
That video will show you how to grab large maps from google... which can be saved and imported into noniGPSplot...
I tried!
phaZed