We are using our $100.00 per paid deposit (Hal)on our Hawaii cruise. We found Hal very willing to work with us. While It stated it was for a 10 day cruise or less, they let us book a 15 day cruise with it. They were also going to allow us to book a back to back Alaskan Cruise if we wanted, we choose the Hawwaii trip over another Alaskan Cruise.
Another thing we found out..If you want to buy a prepaid deposit for someone, you can. The only catch is you need to give them a couple of days to generate a number for them. We talked to them on our last day, we put down a deposit but we not able to do it for our friends.
I wish Carnival had a program like this!!