Hello!
Google Earth is also one of my possible choices for navigation. Works flawlessly on my Debian Etch desktop. I am almost sure, you cannot use it for address to address planning, also there is not any street names.
But Google have some other project - Google Maps (completely online) with street names even of my little town at the edge of the world (be sure not to fall off

) in Eastern Europe. There is also a possibility to overlay sat image and navigation maps. And there comes a problem - they are not alligned, an error of approximately 50-70 meters. Not good in a city.
Another problem there is as it is online service you have to manually cache all maps and reuse them somehow.
And last but not least - legal stuff. As I understand - you may use this service, but are not allowed to change the maps or distribute. So, not good for an Open source project I am searching for. But maybe somebody have tried to do something with it. Could be good as it is global, not only US or Western Europe.