I spent quite a few hours researching Garmin units. I asked a lot of questions and got some very, very good information here:
http://www.expeditersonline.com/forum/tech-shop/29375-gps-systems.html
I also spent quite a bit of time comparing features on Garmin's website (VERY helpful):
https://buy.garmin.com/shop/shop.do?cID=134
I settled on the Nuvi 750 in the end. I have learned alot about how to work with these things since I bought this one and I absolutely love it. I would pay double for another one if I had to, although the prices seem to be coming down (as with most electronics).
Some of the things that I have found to be useful:
ETA function: (pretty accurate). It does take some acclimation, but very useful.
POI (I love the downloadable POI's and this unit seems to have plenty of capacity).
Screen size: is perfect in my opinion. The unit is small enough to not be a space hog, but the screen is plenty large enough to see.
Speaks street names: (some of the lesser units don't say street names)
Where am I feature: My carrier does not use Qualcom and this is very useful for unexpected position update calls.
The ability to edit your route. Once you touch the screen, the unit goes from driving mode to edit mode. You can zoom the map in or out as well as touch and drag the map. To choose a different road, all you have to do is touch the preferred road on the screen (a small window will show the road name/number). Once you've verified that it is the road you want, just lick GO at the bottom of the screen, then click "add as via". The unit will automatically re-route to your preferred road as well as update the ETA and mileage (great way to compare routes for distance/time). I have Co-pilot on my laptop, so when I want to be sure I stay on truck routes, I run the route through the Co-pilot, then edit the Garmin route to match.
Features that I don't really use (although they may be important to others):
FM Transmitter: Don't really need it. The unit is loud enough on it's own unless you have radio or CB on.
MP3, Audio book player, picture viewer: as far as I'm concerned they can take these off and save the memory for useful GPS stuff like POI's... or send me a refund
Car locator feature: I don't usually have trouble spotting my truck at Walmart
.
The 750 does not have bluetooth phone capabilities and personally, I'm happy for that. I have other ways of talking on the phone, don't need my GPS to do it.
Traffic feature: This is a feature that Turtle likes alot, but my unit does not have. Personally, I'm not sure that it would be as beneficial in a truck as in a cargo van (Turtle is in a van). With some expense, I could try this out, but probably won't.
One thing that I could see being very beneficial for some folks that like to sight see on foot is that you can put this unit in your shirt pocket and it can take you to and back from anywhere you like. Personally, I don't tend to stray that far from the truck, but some probably do.
Overall, I love the 750. It does everything I need it to do and then some. I was having trouble making some of my pickups on time simply because I was spending too much time routing them out on the laptop, then writing the directions on paper (and making mistakes). When your pickup times are tight and you miss a road, in a truck, your late. With the GPS, I input the address and haul butt. I've had the unit for about 4 months now and I very seldom have an issue finding whatever location I'm looking for. I seldom call for directions any more. I've learned to just put the location into the GPS and go.
The one thing that I would love to have and have seen the feature on one of the other brands (tom-tom, I think) is lane guidance. This would be very nice.
Hope this is helpful to somebody out there.
