I use Streets & Trips on my laptop to see where I am wanting to go, and to plan my trip and look at the trip options, and see whats on the way. But I would never, ever navigate with one. (been there, done that). You have to take your eyes off the road too much to read and follow one, or about the time you are making a turn, the computer falls over. It's just plain dangerous trying to read a computer and drive through a strange city.
I've got a Garmin 755T, that I wouldn't trade for anything (well possibly another Garmin) It sits right in front of me hooked to the windshield, and I can see both it and the road at the same time, and it very seldom makes a mistake. In fact, it's never made a mistake that was of any consequence. I've made far more mistakes not believing it, than it has made in creating a route. I do like what I read about the new Garmin Duvl 560, and one of these days the price will come down. Then I may need one. until then, the Nuvi and I will get there.
2005 MS 33RS3 #1800
2012 Ram 3500 2X4. If you need a 4X4 you are living in the wrong place
Dick & Dia Downey
and our Itialian Greyhound, Shalamar
The Missouri Travelers