OK, here are some observations based on my short time with this unit. I can see both pluses and minuses to both the Nuvi 200W and the Magellan 3100:
DISPLAY - The Nuvi wins because of its 4.3" widescreen vs. the Magellan's 3.5" display. Both are about the same brightness and touch sensitivity.
MAPS - The Nuvi has clear, easy to read maps using a highly-visible white background, while the Magellan uses muted pastel colors that make the map difficult to read. However, the Magellan shows POI's on the map while the Nuvi does not.
ROUTING - The Magellan wins because of more options, and because it does a slightly better job at recalculating the route should you take a wrong turn.
DIRECTIONS - The Magellan has slightly better advance warning of a turn, and more clearly displays the upcoming turn, even if it is 5 miles away.
POI Database - The Nuvi obviously wins with a larger database, but it is not quite as easy to use.
ADDING A STOP - The Nuvi can add one stop (via point), but the Magellan cannot add any. I don't know how useful this will be in the long run.
MOUNTING - The Nuvi has a much easier method of mounting (clips at top and bottom of screen). The Magellan used a dual T-slot which was difficult to get on/off.
Overall I am satisfied with the Nuvi, primarily because the maps are easy to see while driving (a clear advantage). I just wish it had some of the options of the Magellan, like displaying POI on the map while driving.