When we purchased our Durango last summer I talked the owner into including a Garmin Nuvi-it is a 40LM model.
The few times I've used it did not leave me impressed. The only thing it seems to do well is to predict the time of arrival accurately as long as you don't stray from the route it selects.
For example, last week as we were driving to and from Colorado I had it turned on (I updated it the day before we left, so everything should be accurate). When we pulled off at a Nebraska rest area, about 100' from the interstate it suddenly told us to proceed 140 miles on an unpaved road. No only is there no unpaved road within sight, it didn't have the sense to know we were at a rest area.
When we'd pull off the interstate for gas the Garmin would tell us to do something utterly bizarre, such as "Drive north 72 miles on Blue Bird Road".
As we were visiting friends I entered the address of some friends who live north of Ft. Collins on one of the county roads-they live about 1/4 mile east of S. Taft Hill Rd. We were on in Loveland on Taft Hill Rd. and I would "assume" it would simply take us up S. Taft Hill Rd, and then make a right turn on their county road. The drive is really just that simple. However, the Garmin decided that we should turn right at every major intersection in and north of Ft. Collins. Trilby Rd, Drake Rd, Mulberry St were all right turns that it suggested. I assume it wanted to route us over to highway 287 or I-25-either of which would have taken much longer and had much more traffic than simply going straight north on the road on which we were already traveling. The funniest part was that when we approached the county road on which we had to make a right turn, it told us to continue to go straight ahead rather than tell us to make a right turn. When we pulled into the driveway it at least told us we had arrived at our destination, so it did know the location. It simply didn't have the sense to route us the easiest way.
I'll probably get rid of it at some point. I can do better than the Garmin by looking at a paper map, memorizing the most direct route, and using a bit of common sense.