http://mehere.glenmurphy.com/
This gentleman's created a pretty sweet app to use Google Maps in conjunction with a GPS. I'd be able to use this within a major metro area using my 3G connection and cellphone.
Anyone got any interest in writing a plugin to use it natively within Streetdeck? I've got zero experience with this sort of thing, so it might be a good learning experience, although I really don't have a ton of time to dedicate to this.
If there's a way to keep cached map and street data, or at least download and distribute a complete map package, this would be a pretty sweet replacement nav engine. I'm beginning to hate MapPoint!