My father in law got one late last year. He lives in Galveston, about a 4 hour drive to Austin. He used his GPS unit to guide him to our house. It took him almost 6 hours. It had him going all kinds of out of the way. I don't remember which one he has, but before I buy one I'll make sure it's not the same one he has.
haha I use mapquest or google maps, then look at the map to see what changes I want to make.
My dad has one of those palm things with GPS. I think he's really happy with it and its 400 or less. Plus you can get a OBD scanner for the engine and attach it!