A few months ago I flew my mother and sister to visit in Los Angeles. My sister would be doing all the driving and not knowing her way around worried me a little. While not the best solution I ended up giving my sister and mother my iphone to use its gps while they drove around during the day. My sister would pull over, search for a location she wanted to go, hand the phone to my mom and start driving.
From all I gather they loved it and didn't have any problems using it. My sister also liked the Google street view for previewing the lay of the land so she would recognize things as she got close. Sure I will concede a Tom Tom sort of device would have been the ideal solution but you gotta admit the GPS on the phone did do its job. My 2 cents.