Because of this fact, I find the following ubuntu UMPC components good/bad: netbook-launcher good, maximus good, window picker bad. I want to look at the window picker applet's code to see if I can make the icons larger and the close button larger, but as it currently is, I can't recommend it for the car, it's just to difficult to click the icons standing still let alone when your on the road and moving. Oh, and I did 2.5x the size of the panel to make it large enough for a mobile environment.
It should also be noted, IVI interfaces differ from the mobile interfaces found in phones and MIDs. Those interfaces are still designed with "captive attention" in mind. IVI interfaces cannot demand captive attention by nature. They are close, but the differences do matter. Thus anything that your run on your mobile device in the car will have to be designed for that purpose. You can still get away with running mobile apps in IVI environments, but it's probably not going to be optimal.