I just booked my airfare for my cruise on the Valor in May of 2005 - 8.5 months away. I like to do that because then I know I have one less thing to do / buy come next year. However, when you do that, it is a good idea to keep an eye on your flight times every once in a while. They tend to change a little when you buy your ticket that far in advance.
Have fun on your cruise!