Sadly, I use my wife's bluetooth ipaq for car GPS. With Z although mapping works that can be dangerous (looking at map while driving) without the realtime voice giving you directions and recomputing the route everytime you make a wrong turn. Points of interest (restaurant locations,,,) is another key feature.
If anyone decides to be seduced by the dark side, bluetooth ipaqs like the 1935,45 are dirt cheap on ebay and bluetooth gps (make sure you get additional antanae) is fairly reasonable. Combo of iguidance software (Fry's) and microsoft maps (better POIs) works well for me. While I'd rather use my Z this is still much cheaper than standalone GPS that comes with snooty cars. Wife is expensive.