I would bet that when they implemented the fuel charge last time they saw a corresponding drop in on board charges because many people felt as Dwayne did- "Well that is less beer and Casino allowance then" So they may have taken fuel costs into consideration in raising the cruise fares so that people don't fall into that mode.
In any case I hope it doesn't happen either. I would rather pay more for the cruise up front then to find out a little bit before my cruise that it is going to cost me $200 more than I expected...
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