Hello ! I'd like to give you some information from "behind the scenes"... as I'm working on a cruise ships. May be some of you already had figured out the whole system by yourself, but that's how I see the things. Pre-paid tips is not always fair distributed...The " first line" service personal is underpaid, those are employees working for $ 50 a month, with no day off, up to 12-14 hours a day. These are the people to make your cruise more enjoyable. What often happened, to the waiter, for example, is that at the end of the cruise he is getting tip only from 6 out of 12 guests, because of table changes, special restaurant dinning options, etc...We assume he provide an excellent service. If the cruise was 14 or more days?? It is very annoying .. The petit officers- like head waiter, etc.- they have good salary anyway,and better living conditions and they don't need to do the hard job of your waiter, so they have enough time to "please"you, meanwile to give hard time to your waiter... I have to mention that during the lack of space onboard the cruise lines employ as less personal, as possible, often giving more duties to employee than he can manage with- THE REASON #1 FOR POOR SERVICE.
I exclude some workers I've seen that are not responsible persons, the only way to treat them is to write your comments and hand them to the front deck.
In my oppinion tipping personally at the end of the cruise is the best you can do.
I appologise for the mistakes, English is not my first language.