I love these guys. $6 each way to the Strip. $12 round trip. Depending on how many people you have, it's cheaper than a cab. Actually, taxis take no more than 4 people and cost about $22-$25 plus tip to the Strip. Its $24 on the shuttle one way for 4.
They have always been on time and they run continously. Obviously, it takes a little longer to your destination due to the multiple stops, but, the ride is cheaper and just as smooth.
They're also very accomodating when you're too drunk to call them the night before your pickup date.
Executive is my shuttle of choice in Vegas.