Believe it or not, I've had to use the Platinum "Override" (or Guarantee) twice this year already. I used it last week in Orlando at the sold-out World Center to get a room for a colleague who was summoned to a conference at the last minute. I put the reservation under my name, but they let him use the room. I already had a room at the resort, so they did question me about that and whether I needed both reservations. But there were no problems at all. Yesterday I tried to get a hotel room in downtown Chicago. I tried Marriott.com and there were no rooms anywhere closer than Midway airport! Then I tried hotels.com, and there were no downtown hotels available there, either. So I called Marriott reservations, and they couldn't find me a room. They I called the front desk of the hotel I wanted, and they couldn't find me a room. But they suggested I call Marriott Rewards, so I did. They said there was a "special event" (the Ideal Home Show) and all of the downtown Chicago hotels had been approved for a "corporate override" which trumps the Platinum Guarantee, so no room for me. But then they transferred me to another person to "double check" with the specific hotel I wanted, and that person put me on hold for about 20 min. and got me a room at the JW (which was my first choice, although I'd have been happy with ANY downtown Chicago hotel of any brand, Marriott or otherwise!). The rate was high but not out of line for that hotel, so I gladly took the room. I got an email a few hours later confirming the reservation, and it's showing up on my online account. I tried to get another room for a colleague, but all they could get was one room. So I guess my colleague will be staying out by the airport. So, I relay this story to show that persistence pays off! I had to talk with about 4 people and really keep prying to see if we'd exhausted all possibilities, but I finally found the right person to help me. And I am very pleased with Marriott Rewards!
Rates at that place really vary from time to time. I've gotten rooms as low as $159 when it's a weekend. During the week, rooms are usually pretty high. Last time, I paid $499 for a weeknight stay. Sometimes you can get in during the week for $269 or so. This time it was $589 - ouch!!! But it's worth it as I have meetings across the street and really need to be close. It is also a really lovely hotel with great service.
Update: I got the LaSalle Suite at the JW Marriott Chicago. It was fabulous! 2 bathrooms, a living room, wet bar, walk in closet, etc. Because of the snowstorm in NY, some guests didn't make it to Chicago, so the hotel didn't actually have to "walk" anyone after all. So I was glad to hear that.