I don't think it's a good idea to use android as an OS for the car for several reasons.
1) you are locked into using android specific APIs because android does not use many standard Linux APIs (ie, like using gstreamer for audio).
2) you don't gain much by using android. A lot of the android apps will have design issues that make them incompatible with in-vehicle environments. That makes the apps all but useless. So if you can't take advantage of all the nice cell phone apps, why use it? If you just want something that boots fast, use Moblin or LinuxICE and build on that. At least you'll be using standard Linux stuff that won't be tied into a specific platform.
3) Google will kill Android. I could be wrong but it seems like Chrome OS is their new baby. I wouldn't be surprised if Chrome OS replaces Android on the phone and everywhere else. In fact, the android "experiment" may have just been another poke at Microsoft to **** them off. To add, WebOS and Maemo are superior Linux-based platforms on the phone and Google knows this. It's easier and more profitable for google to be on Apple's, Palm's, Nokia's, Microsofts, etc phones by making deals with them than it is to make just-another-mobile-phone-os.
just my two sense