I haven't tried it but I do agree. I've long believed that the car is a logical extension of LinuxMCE. LinuxMCE allows viewing of all types of media, control of devices (doors), linking with cameras (backup cam), and integrating with other applications (GPS Nav).
A nice feature would be automatic synchronization with your home linuxMCE system by downloading movies, shows, audio, emails to the car hard-drive over wi-fi. One of the problems seems to be the inability to have a non-diskless MD, but having a full-blown core in your car might be overkill. So I think there needs to be a new system type in between a core and a MD that can run without constant connection to the core. Another benefit of LinuxMCE is the possibility of using your phone to start your car and control the audio/video from the back seat, although there are obviously security problems with Bluetooth that need to be addressed.
A couple linux car computer projects are:
I think the above projects are open source so they can be used as a starting point for adding drivers and GPS navigation.