If you are wondering what kind of activities they have on a 3 day cruise? I think they try do offer everything they do on a longer cruise (except less shows obviously) and leave it up to you to pick and choose what you want to do.
So be careful not to try to do everything that is offered or you will exhaust yourself.
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