We just arrived today. I had gotten an email yesterday a couple of hours before we left to the airport, with instructions to go to the radisson blu across the street.
We arrived and a couple Hyatt were camped out in the lobby and confirmed our reservation. She talked into her walkie talkie and stated that we had been set up at the Hilton Park Lane nearby. I was too tired to argue, but they did say that they were covering the cost.
We were staying on points, so I was concerned about getting full value, or if they were just going to refund my points and leave me on my own. But they covered the cab to the Hilton, and we still got some platinum amenities (high room, great view, etc.)
The Hilton park lane is a really nice place ($486/night when I checked today), but I thought that Hyatt handled things really well. I was annoyed that I couldn't just confirm the new hotel before hand so we didn't have to trek to the radisson and leave again, but I also understand that during a crisis you deal with the problems right in front of you first.
The Hilton confirmed that everything was covered, and overall I'm really pleased how it all ended.