I've used this shuttle many times and have always made it to and from the airport timely.
The shuttle service is $6 one way. I recommend purchasing a round trip service for $12 so that you can call in your pick up without having to worry about how to get back to the airport. They will give you a receipt or a poker chip with the number to call to arrange a pickup. Make sure to call at least 24 hours in advance. You can tell them your flight time and they will figure out when you need to be picked up. Its usually 2-3 hours ahead of your flight time.
The downside to having shuttle service is that you need to sit and wait in the shuttle until it is completely full before you can leave the airport.
I highly recommend staying at the Venetian or the Palazzo. This hotel was the first to be dropped off from the airport and the last to be picked up to go directly to the airport.
So glad they have this shuttle. Saves $ so you can have more to gamble with!