The Shake Shack was open today for previews. I don't know when it opened; I'm usually not in the area. But my guess is recently, because the line was much shorter than what I had read about. It took me about ten minutes to order and receive.
It appears they will serve hamburgers and shakes. All they were serving today were hot dogs (three varieties, Chicago, garden and taxi, whatever those are), ice cream and drinks. They were also offering a 20 percent preview discount.
My Chicago hot dog was perfectly fine - the roll was poppyseed and the toppings seemed fresh and accurate, from what I know of Chicago hot dogs, but the hot dog itself was nothing extraordinary, though it was fine and 100 percent beef, for those who care.
Lots of tables outside to sit and eat on this lovely temperate day.