Not counting driving on the wrong side of the roads. I wonder if google cars' AI only needs a "Drive on the wrong side of the road in this country" command, or if some more complex programming is needed.
If you look at Google Maps (at least on the desktop,) there's usually directional indicators on odd roads and in any directions in the UK you'll notice how the blue line goes clockwise around roundabouts instead of counter-clockwise like our friends in the rest of the world