Just got back from the Benoit New York. Used Centurion Concierge services to book a table, and asked them to please confirm the benefits.
For this location they were:
-Welcome Drink (either Champagne or restaurant's signature drink)
-Amuse Bouche
-Kitchen Visit
-"good-bye gift"

We mentioned we had a reservation for tonight when we entered the restaurant, and were escorted to our table. No words about the Centurion reservation were made. Waiter handed in the menus and left, without mentioning the benefits either. When he came to take the orders, we mentioned it.. but he had never heard of it.. we showed him the emails (I always make reservations for things that have benefits over email, so I have proof in cases like this) He then came with the glasses of champagne, an "amuse bouche" that every table had and bread. Food was excellent, everything was fresh and delicious. No kitchen visit was offered to us, and we didn't want to ask (we really wanted to visit it) for the visit because if it was not offered, we thought it would create an awkward situation. Upon leaving, they handed out a "good-bye" gift that everyone else who ate here received.

Essentially, dinner was great. It's a really good restaurant and prices are not too high (menu is available online). But im very disappointed at Amex Centurion.. First for not making sure the benefits would be given, secondly because after the "recognition" of the benefits, we realised that everyone else got them.. so they are not Centurion benefits, and Amex shouldn't "sell" them as such..