BTW, slightly off topic but related.
My Nuvi 360 does not have routes, but it does have Custom POI (Points Of Interest), which work as a decent alternative.
I found a relatively easy way to design routes using Google Maps, then convert them using Google Earth into Custom POI coordinates file.
Essentially this file is a CSV file (Comma Separated File) with POI names and coordinates (long & lat).
I wrote a small XSL (sorry, technical computer stuff
) file to transform the GoogleEarth KMZ file (which is really XML) to that CSV..and the output is a numbered CSV file.
So each coordinate starts with a prefix (01_<TITLE>, 02_<TITLE>, etc.)
Then a quick upload to the Nuvi using their free utility, GarminPoiLoader.
Anyway, works like a charm.
One does have to select the next POI when the last POI was reached, but if the POIs are not too close to each other you don't have to do it too often. It also makes the GPS route less automatic which I like, as it remind me of navigating with a map - the rider has more control.