I have a couple Garmin GPS units, and the only complaint I have is the software for interfacing with a PC is nasty. The units we bought at work involved our IT people and Garmin customer service to finally get them to work together.
I also use Delorme on my laptop in my work truck, and love it. Before I spent a bunch of money on a GPS unit soley for my vehicle, I would look at a good PDA and the Delorme software with Bluetooth. Big screen features of a PDA, and a tool that has more than one use.
JMHO