I've used their concierge. I was making reservations and plans for a client of mine to fly East and stay at a hotel near Newark New Jersey. I asked the hotel about an airport shuttle and was told by the bellman and the front desk manager that there wasn't one but they could arrange sedan service for $100. I tried find information on my own using the internet but no luck. I called the AMEX Platinum Concierge and they found a shuttle and e-mailed the answer to me the next morning.
However, on a later service, they were unable to get tickets to a sold-out B.B.King concert in Denver, Colorado.