My opinion is it works and that's about it. I am right handed and drive a right hand drive car so it means I have to use my left hand on the screen. Car movement and me not being the greatest with my left hand anyway means for me it can be a bit hit and miss getting the right buttons. My plan for my next car puter is to try and get a usb version of a touch pad like is on a laptop. I reckon I can place this somewhere that would be much more relaxing to use and more accurate because of it.
This is just my opinion and there are loads of people out there that would swear by a touch screen.