I'm starting the Southern Tier Route next week from Florida to Ca. I just got my new Garmin Dakota 20 GPS, loaded it up with City Navigator North America Maps, and loaded the GPS route coordinates from Adventure Cycling that you get here: http://www.adventurecycling.org/routes/southerntier.cfm
With all the POI's that are in City Navigator, and the navigation and helpful points from Adventure Cycling's research I hope to use the GPS as my primary aid to navigation.
I did order the paper maps for the first section of the route to see how it compares, and have it in an Ortlieb map holder on my bag/bars.
The Garmin is mounted on a RAM bar mount, next to my iPhone and a Cateye computer. Looks like the Starship Enterprise, but I am a gadget enthusiast.
I am running a hub dynamo that charges up extra batteries for the GPS and iPhone, so hope to have power for he trip without needing to plug in too much.
What I like about the GPS is that I can now relax and enjoy the ride, knowing that if I get off course/lost/distracted/delayed I can let the GPS reroute me back on course automatically. I will also have a track of my ride with statistics, blah, blah.
I'll post how the dynamo charging works when I have some experience.