It definitely failed a friend of mine at the PHX Airport Marriott. He landed, called, and was told it was on the way. 30 minutes later, still on the way. Another 15 minutes, and it was "15 minutes away". Finally I went to the front desk (I was waiting at the hotel for him to arrive) and they claimed the shuttle operated on request only and that no one had called for it in the past hour. So it hadn't even left the hotel! It got dispatched, then 30 minutes later my buddy was still stranded at the terminal. FINALLY I left in my rental car, went to the airport and picked him up, and was back in 20 minutes. Of course I would have done that right away had we known the shuttle was going to be such a debacle...