Like Dave said, it depends on when I am flying (the day of the cruise or early) AND if I plan on using cruise line provided transport.
It used to be that if you had cruise transport, that they would claim your bags at the airport and you wouldn't see them again until they were at your cabin door. but now with the new security rules, you have to claim your bags anyway.
If I am flying the day of the cruise (which I don't do anymore unless absolutely necessary) then they go on at home and then checked to make sure they stayed on after the flight.
If I am flying in early I wait and do it at the hotel before going to the ship.
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, Celebrity Silhouette 2013