Cute (iPhone, etc) app which tells you where to stand on the subway to arrive at the right exit.

Taking the 1 train uptown to 28th street? Get on right behind the middle conductor. Need to transfer to the L at Union Square from the N downtown? Ride in the 1st car. Detailed diagrams eliminate the guesswork and frustration from your ride, making your subway trip easier and faster.

The developers rode around the city for 10 weeks to build the train maps. Unfortunately, the app becomes useless if it actually gains traction. The cure is to not be in a hurry, for which there is no app.