I wonder which car manufacturer who will be the first to incorporate an iPad into the dashboard of a car. We know that car makers are keen to include iPod connectivity in their cars, and iPad seems like the next logical step. Sure, everything I'm about to write applies to any given iPhone or even iPod touch, but with the iPad, you get that nice big screen which is why I think this would be desirable.
Think about it and it's a pretty neat thing. The best thing for the car maker would be to make it an optional thing. You'd order your BMW or whatever brand it is and in the dash you have a 10 inch plate, ready for an iPad. Only, if you order it without it, you get an ordinary car stereo plate inserted into the space. It's exchangeable, so if you change your mind, it actually disconnects and you can then insert one of two iPad-optimized inserts. One for a more permanent fixture. I.e. it blends in that awesome 10 inch screen into the dash and it stays there. The other option is to have it easily removable. You can click in your own iPad into place, and take it with you if you please. With iOS 5 and data syncing via iCloud, I'd think this wouldn't be a necessary thing. All your music, photos and such sync to your "car iPad". And the more permanent solution would still allow for disconnect if you want to sync large movies to it for some reason.
As for how it would be used, that's where the sweet stuff comes into play. Using the 30-pin connector, you can have a button on the dash that launches the "BMW Dashboard app" which is a free download from the App store. Using that app, you can control most of everything in the car. Sure, some basic functionality would still be available via hard buttons and knobs on the dash, but the app would provide a much more intuitive way to set up the radio, stereo equalizer, suspension dampening, automatic distance to cars when in cruise control and god knows what. When you put the car in reverse, the app would launch and display the video from the rear video camera.
When not using the car app, you'd download your preferred GPS and have a 10 inch GPS screen on your dashboard, instead of using the manufacturers crappy GPS solutions, or an on-dash solution. The car would obviously tap right into the audio and you could listen to iPod, podcasts, Pandora, Last.fm, Spotify and whatnot on the road.
Using airplay, movies on your iPad would play on the two headrest screens for your kids, while your GPS runs on the iPad. You can even initiate Facetime calls from your car if you'd like.
Where do I order this car? :)