iGuidance for GPS (though I notice there's a GPS button already) and a handful of utilities for tuning my ECU - one for reflashing, two for data logging, a real-time dashboard, and a utility that shows learned parameters in the ECU.
I haven't hooked up my CarPC to the car's speakers*, and I don't do any networking other than wifi in my garage, so I wouldn't be using the buttons for radio, music, video, tv, weather, gas.
Then again, if the phone integration works well, that might push me to finally integrate the CarPC and stereo. I really want that, just haven't seen good software for it yet.
* My factory stereo is a six-disc MP3 CD changer, so I just leave it on shuffle and my music needs are met.

