The past few trips to Vegas the casino host has arranged for transportation for me to/from the airport via the hotel/casino limo. I always tip the driver but I'm not certain what should be a customary amount. They seem appreciative, but I guess I wouldn't expect them to show me their disappointment. So.. what would you consider a reasonable amount for the driver? Would the amount change based on the number of people in the Limo (usually it's only me, but sometimes it's a party of two)..