Carnival has no limits per se (just a limit on the size of carry-ons); most other cruise lines either have no limit or say you are allowed a "reasonable" amount of luggage.
NCL's current limit (2 bags, 50 lbs. each) was posted above.
However, in this thread from 2008, a poster quoted NCL's then-limit as "Each person is allowed up to 200 pounds of personal luggage on board."
SO...maybe need to take as much luggage as possible while we still can? 50 lb. limit next year?