Well- I'm not sure if anyone has completed an install yet because seeing as the MM just hit the market so alot of stuff isn't ready yet- but there is some stuff in the works. so lets go through this-
*Touchscreens: Lilliput and Xenarc (2 major brands for in car use) both have Mac OS X drivers. Here's a link:
Xenarc ->
http://www.xenarc.com/download.html
Lilliput - ->
http://www.egalax.com.tw/Download.htm
*GPS- GPS is less supported than PC but we have Route 66 and I believe most USB or Bluetooth GPS recievers will work with the Mac. Don't take my word as truth though- look around the forums for a sure answer.
*TV Tuner, AM/FM- There are external TV Tuners coming out from ATI and some other company. They were announced at Mac World. For AM/FM Belkin (I think) has the shark fin thing that plugs into USB and acts as a radio reciever.
*Power Solutions- This is what I'm waiting on to install mine- Carnetix is working on an adapter that will work with the MacMini so once that hits the market we will have power for our Carputers that is as good (I think) as the Opus of the PC world.
http://www.mp3car.com/vbulletin/maccar/40765-dc-dc-car-power-mac-mini.html
Issues with install (heat, pain, etc): Well, As I mentioned before no one has installed a Macmini yet- (that I know of) so the heat issues and mechanical issues aren't known yet.
Well- that's all the info I know- I hope it helps. Also try heading over to
http://www.carputermac.com
it's a fledgeling crowd but we're growing more and more.
Peace
Michael