Poor service from impatient and unfriendly cashiers, phone operators, and drivers. Waited half an hour at McCarran for a shuttle to pick us up.
Called the night before to schedule our return trips - three different groups of us left at three different times. For the first two groups (leaving Sunday morning), the shuttle hadn't arrived at our hotel after half an hour and they ended up paying for cabs so they wouldn't miss flights. My shuttle (on Sunday evening) hadn't shown up after ten minutes, and when I called I found they had booked the shuttle for a different day. There happened to be a shuttle at a neighboring hotel, so I was fortunate enough to not have to pay for a cab.
I suppose that $12 for a round trip to a hotel on the north (far) end of the strip from the airport is a good price. But if you have several people or are staying closer to the airport, just take a cab. And if you take Gray Line, be sure you leave a LOT of time between your scheduled pickup and your flight, and call to confirm your pickup.