Have had a Garmin GPS V for the last four years (2002). Used it mostly on-road and the device has probably saved me 10's of thousands in gas and time driving in LA. GPS V was also one of the first that was WAAS-enabled (basically, higher navigational precision; apparently accuarate to within a few feet)
But a couple of things could stand to be improved:
1. It has 19mb storage. This covers maps and points of interests for the city of Los Angeles and that's about it. Need to drive out of town and you have to pull the maps from the included DVD.
2. Processing speed is a little slow at times, given the pace of traffic. But, you can adjust for it without too much difficulty. Enabling WAAS slows it even more, however.
3. The update DVD (ie. new points of interests; in four years time, a lot of stores/services in your city can come and go) runs 50-70 bucks (little pricey)
I don't really mind that the display is black and white and there is no voice prompting. Unfortunately, the GPS V has been discontinued by Garmin!
TIP: I paid $500 for this thing at a West Marine in 2002. You can buy them nowadays for a couple hundred. If you buy one that was manufactured in 2004 or 2005, you will be getting one with the DVD that has the latest Points-of-Interest updates. GPS Vs made 2003 or before probably won't.
If you don't want to spend a ton of money and use a PC (GPS V not Mac compatible) GPS V is a good choice. If you have the cash, I'd probably shop around on CNET or Wired for their editor's top picks for 2005-6. But, those selections can run you $800-1200.