You can use your free night cert at the Plaza but it ain't easy. When I tried to use one in April the earliest date for a free night was in September. So book far ahead since they have very limited availability.... 6 months minimum.

I haven't stayed at the plaza since the recent transformation to a condotel, but reviews I've heard don't really live up to the price you need to fork out. If you happen to stay somewhere else and save a few $$$ head to "Per Se" for a dinner you won't forget in this life!