Yeah, you can't watch a DVD while driving, but GPS, heck half the cars come with GPS stock.

It would be illegal because its in direct view of the driver, its an distraction to the driver and others. You are not suppose to even have satallite radios or gps on the windsheild blocking your view, they are suppose to be off the the far side. Why not get like a rear view mirror with a screen built in instead.. a huge screen like that will probably look terrible.

they'll knock you if they think you were watching a movie or something on it while you were driving, and often it's the officer's discretion. A lot of people I hear get away with switching a movie or whatnot to a nav screen before the cop gets to their door. Navigation systems are fine, it's entertainment systems that they charge for. Like I said though, a lot of it is not written law as far as multi-use systems go, so often it is officer discretion.