What are some slick things we can do / have done with Android tablets as CarPCs?

As the prices come down and the technology becomes better, I think Android tablets become a clearer choice for use as CarPCs. I thought it would be nice to document some of the current things we can do with the tablets as well as what should add value and be theoretically possible as well as what an implementation may consist of.

I, for one, am really interested in the CAN Bus system and believe we can garner some great benefits from being able to transmit and receive on it. I'm not talking about the OBDII part of CAN, but rather the door lock signals, A/V over CAN (I'm pretty sure I read about this somewhere), steering wheel controls, etc. Each vehicle will be different, but I think it should be very possible to design a common hardware interface (Android->ADK->CAN) and an app that can help us record and replay signals we're interested in.

Another aspect I believe we should always keep in mind is security. If we begin taking information designed to be transmitted over wire and begin exposing it to a device with wireless capabilities, we need to consider any and all potential vulnerabilities.

So I purchased the IOIO from sparkfun.com and modified the HelloIOIOService app to listen for a state change on one of the digital pins (+5v=HIGH, 0v=LOW) using a voltage divider (discussed here) with input coming from a harness in the car that gives +12v when ignition is on and 0v when it's off. This alone is a fairly expensive way of turning the screen on and off with ignition (although, it allows for much more complex logic than something like the relay solution.)

I also just purchased an SPI-to-CAN module to make the IOIO earn its keep.
I'm hoping to glean some information about how to interact with it from some existing projects. I think all of the info is there.
Arduino + Controller Area Network (CAN)
canduino
Hacking Your Car (loads of info)
Interesting Presentation on CAN (with security considerations)
IOIO SPI Doc

I see this thread is getting old. But have you investigate Tasker for Android? You can set yourself up with that and a car docking station and have your table start and stop according to ignition signal.

Check it out. They have an active Google forum with just this kind of thing in it.