Tom,
I too enjoy frequent comps from Harrahs - they are based on past frequency of visits, and play. Since they offer "free nights", you don't have to drop a dime, and you still won't be charged for the room; of course, if you don't gamble, future offers may dry up!

Many places don't require a deposit, unless you want to charge to the room. Charging to the room, BTW, is a GREAT way to get everything comped - should you hit a monster run.

If a place had offered me a free night (like Caesar's did to you), but they required me to put up a credit card; I would have specifically asked if I would get charged for the room if my money were to run out early (and I didn't get my normal amount of gambling in). If the answer was yes, I'd refuse and threaten to leave and never come back! Either they were offering you a free room, or they were offering you a CHANCE at a free room. BTW: EVERY casino already offers you a chance at a free room; gamble enough, and they are gonna comp not just the room, food & beverage, and maybe even a shopping spree! If this had been a printed offer, I'm sure there was fine print indicating it was just a chance at a free room, and warning that you might be charged if you don't play at the same rate as last time...