Join Date: Feb 2006
Location: Coastal Maine
Bikes: Specialized Tricross Comp, Lemond Tourmalet, Bridgestone MB-5
With my limited time with the Garmin 200 in a car, I'd say it's doable. The unit is extremely accurate even at slow speeds (<25 mph) in a car. You can zoom in and out of the map plus also has turn-by-turn, complete with disembodied voice telling of the approaching turn. I can't speak for the run time, but I believe it's 3-4 hours.
I like it mostly because it's so easy to use. Without instructions, I was able to figure out the interface very quickly.