There is a solution on the way. TomTom's car kit is a cradle with its own GPS unit inside and it is suppose to work with the iPod Touch. In truth, when do you really need a GPS anyway when you live in the cities? If you said "in the car", then you're right.
Watch the video demo and you can see just how seamless TomTom has made the car kit for the iPhone and iPod Touch. It even comes with a charger and a connection to play your music in the car.
Impressed? Well, it will set you back $200. $100 for the TomTom app itself and $100 for the car kit.