It all depends on the service I get. It is a tip after all. Tips are suppose to reward good service or above and beyond service. Unlike land based services, uncle Same isn't assuming they are getting a 15% tip, so if their service is not good, they don't get a tip (or at least no extra tip from me). But if I see them doing extra things to make my trip more enjoyable or I feel my family is making the stewards or waiters work harder than normaly I will give them extra.
The bar waiters get 15% from the receipt, so unless you don't feel that is enough, you don't need to tip them. If a bartender serves you drink, check the receipt to see if a tip is included. Sometimes when the bar tender hands you a drink they don't do the auto tipping.
$2 to $3 is typical for a room service call unless you have ordered a huge tray of food where you might want to go to $5
Again MOST of the service crew is covered in the auto tipping policies, so tip as you see fit.
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