The only downside to the eepc is size. At least you can get one of those arms similar to what you see in police cruisers to mount your netbook on. I just like the idea of a mini tablet PC much better since it is touch screen, has GPS, and you can get internet with it too. Granted, you can do all these things with the eepc too except for out of the box touchscreen operation.
I assumed you were going to use the eepc with an existing HU and an aux in. Life really gets tricky when you want volume control, crossover capabilities, and all that other fun stuff.