Yes, the new passport requirement goes into effect at the end of this year. If you cruise is before then, you only need a birth certificate and US identification. But, if you plan on doing any travel outside the US early next year, I suggest getting you passport now do to the rush that is sure to happen next year.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007