Is there a way to input GPS co-ordinates into the iOS6 Maps app? In Google Maps and the iOS-5 Maps app you can search for co-ordinates such as "loc: N 42 14.768 W 071 02.156" (note the lowercase loc). In the new Maps app this fails with No Results found. Is there another way to enter GPS co-ordinates or is this another missing 'feature'?
Yes. Omit the "loc:" and just enter the coordinates.

40.748342, -73.984606 will drop a pin right on the Empire State Building.