I was thinking of putting a computer in my car for a couple of reasons:
I've got one that will already fit with ease and plenty of replacement parts for it. By putting in a computer, I can tune my Electromotive computer without lugging the laptop around. Not only do I get the ability to watch DVDs, but I can also play mp3's and update them by just pulling into the garage. I'm going wireless in my new house because I don't want to tear down freshly painted walls to install cable. So, all I have to do is pull in the garage, connect to the network, and get the latest songs I want/browse the internet for whatever.

Doesn't get much better than that.