I'm staying at the Berlin Marriott this weekend. I went on their website, chose a rate with breakfast, and was very happy with it. Then I saw a thread about the corporate rates and went onto the Marriott res site and typed in the code of several corporates. Lo and behold it brought up exactly the same rate as I had booked. The only exception was Marriott employees and I wasn't happy choosing that. In the event it would have only saved me a few Euros.

I guess their promise to provide the best available rates actually means something.