I've had a 7" touchscreen in my truck now for about 2 years. I started with a Lilliput and loved it. However, when I tried to hardwire it into a powerstrip (12v), I fried the unit. I bought a Xenarc to replace it. I preferred the Lilliput, personally.
If you'd like to read more info on it, here's a link to my system:
Truck laptop / GPS setup