Ok here is a few functions that I enjoy with my carputer.
Music: Of course, all of my CDs have been converted to MP3s. Instant access to all my music. Much better then a changer. If I feel up to it I can tune into one of the 10,000+ internet radio stations.
GPS is a bit better then any other GPS. It is on ether the 8" screen (Big) or on the 7" next to rear view. What do you like better. Those 2d images on the GPS you buy prebuilt? What if you had Google Maps? I prefer to have google maps in satellite mode
Video, You ever have real time conferences with someone using instant messenger or VOIP. My friend stays in contact with me over VOIP and they get to see my ugly mug driving or the road where I'm going. Mom likes it when I drive to her place, she knows where i'm at on the road. No with instant messenger I had the problem of driving and typing. I switched to a blue tooth headset and vista's speech dictation. Now messages come over and spoken, I speak and the message are dictated. Disadvantage there is, you have to be commanding in sending new lines. IE saying "Enter" to hit the enter key. Accuracy is very good when using a Jabber noise canceling blue tooth headset. Night time driving is a blast if you turn off your headlights and turn on the infrared foglihts. The FLIR shows everything. No need to look at the road then! ;)
Some of the software i'm working on at the moment. If you are low on fuel, you can read the tank level via OBD value. have the computer point out some fuel stations with the cheepest price and then point them out on the GPS. Or when I come home at night I turn down the stereo. Well I have it now turning down the stereo automatically just before my garage.
I have such big plans for this thing and I love to tinker. Some times a few min after work I will hack at some code for a new feature. Its like having a new toy every day when you make changes. You have to get out of the mind set that your looking at a computer. Your not your looking at nothing more then the same thing as a high end touch panel stereo. But I have a huge advantage over the touch pannel stereo, I can reprogram it any way you can a computer. Now as far as cost. Yes its a lot. I have well over 4k invested maybe even closer to 6. But if you add up that high end stereo, GPS, back up camera. you get up there with the money. Where I have it all in one package where I can integrate between functions and the car.
Lastly the biggest one is just because I can. Why not? I enjoy the hell out of it.