My fiancee and I booked this hotel 2 months prior to our visit and when we arrived the hotel manager - very pleasant he was - informed us that their wasn't any rooms available at the hotel!? To which he immediately apologised profusely for and arranged prior to our arrival to stay with the Westin hotel 5 min's north of the St. Regis.
In the interim he ordered the concierge to organise our hotel transfer via a private limo and the bar/ catering staff to serve us complementary drinks and food (no limit on spend, type or quantities) to apologise to us for their huge mistake.
Before we left he informed us that due to a diplomat staying longer than anticipated they had to give up our room to accommodate this. However, he wished to bring us back on our last night as the diplomat would've left by that time and will receive a complementary room upgrade to a Junior Suit, complementary Champagne to our room and to dine in their restaurant (of which I worked out the final bill on the night come to over €300) as their guest and a personally hand written letter from the general manager apologising for their failings to us.
Overall, our Westin hotel was still grand with high ceilings and a good concierge service, even after spending only one night in the St. Regis hotel I would've certainly preferred to have stayed my total 4 nights with the Regis rather than the one, however, I must admit the St. Regis sure knows how to apologise to a customer.
Would certainly stay with them again.