I don't know if this was clever planning by someone at Apple, or just happy chance, but it looks like that new iPad Mini we're all so excited about (sort of like how the world lost its shit at the release of fun-sized Oreos) is almost exactly the right size to fit into many car's dashboards easily.
Normally, knowing Apple, I'd think this was deliberate, but the dimensions are just off enough to make me think it's more chance. If Apple wanted to do it officially, it'd be exact— that's the manner in which they roll.
As it is, it's pretty damn close.
The big rectangular hole in most modern (late 80s and up 'modern') car dashboards for the head unit is 7.2" x 4.22". This standard is known as Double-DIN, because it's basically two stacked DIN-sized holes, which is the size of a standard radio head unit. The official standard name is ISO 7336, and it's called DIN after the German standards bureau that first adopted it officially, Deutsches Institut für Normusomething.
From what we learned today, the iPad Mini has a screen sized (diagonally) of 7.9", with an aspect ratio of 4:3, and pixel dimensions of 1024x768. That gives us a screen size of 6.3" x 4.5". Factoring in the bezels adds a little bit to the size, giving us an overall total dimension of about 7.8" x 5.3". That's bigger than stock Double-DIN, but not by so much that other vents or controls on most vehicles would be obscured.
I'm predicting there will be a number of in-dash dock solutions soon to easily place an iPad Mini in your dash, and remove it easily. The iPad Mini could make a great combined nav system (just maybe not Apple Maps yet), music/video player, and potentially much more with the right connections and apps. Docks that connect power and audio output will of course be the norm, but it should be possible, for example, to get other inputs to the iPad, say from the OBD port to allow for advanced diagnostics and certain pet projects of mine. Maybe even clever folks will figure out how to get input from your car's backup camera or something to save the video to the iPad? Who knows. It's a little computer you can about fit in your dash— the possibilities are huge.
If the dock route is too clunky, and you have the money, permanent installation should be quite easy, as the screen itself should just about fit in a standard double-DIN hole, meaning the iPad Mini can be mounted behind the outer frame of the dash hole, and trimming should be very minimal. I'm sure this will be a popular solutions for lots of DIY car-modders.
(Note: When final exterior dimensions are released, I'll update and confirm this should still work!)