I have always done ours because our PVP said to, and after reading the boards, I am glad! People who have not done theirs have spent an outrageous amount of time at the check in desk so I would say..do it! It is easier to put all the info online than to have to drag all of your papers out while standing at the desk....
Glory - 2006
Liberty - 2007
Pride - 9/28/08 - 30th anniversary cruise
Mircle - 12/7/08
You don't have to do it online, but you will get on the ship faster. When you get into the check in desk and you did your funpass all they have to do is check it. If you don't do it they have to enter everything in.
The website is funpass.carnival.com.
Carnival Dream for Thanksgiving
Eastern Caribbean- 11/20/2010
Carnival Ecstasy (4 Day Baja Mexico) 2003
Carnival Pride (7 Day Mexican Riviera) 2007
Carnival Spirit (8 Day Exotic Mexican Riviera) 2007
Carnival Freedom (7 Day Western Caribbean) 2008
Carnival Elation (4 Day Baja Mexico) 2009
Carnival Spirit (7 Day Southbound Alaska) 2009
Yes, do it ahead of time. I don't even think they asked to see the printed copy at embarkation. Just our ID's and they had all the info they needed. Took a lot less time to check in that at the hotel the prior day.