I've booked two Hyatt mistake rates for premium suites and both times they were honored, Grand Hyatt in Seattle for Onyx suite emailed me saying they could cancel it but they weren't going to.

FYI to the person above that mentioned Beaver creek, they makes mistakes all too often during summer months for me to believe they are actually mistakes. I only booked it because my friend lives in Vail and funnily enough she stayed in the suite because she was interviewing for a job there, she got it but declined.

Another tip for anyone else who cares, if you book a mistake rate but don't have travel plans yet... book each night individually that way you can modify dates etc and cancel if its a refundable rate. If you book 5 nights under one reservation and want to change it to 4 they wont let you for you example but if you book 5 one night reservations..