As posted above Carnival calls it: Cruise Elegant Dining Dress Code and they are only "suggesting" a sport coat. Suits and ties are optional. Having shelled out $300 a night for my floating suite with a balcony I really don't think I should have to feel guilty about not dressing up enough to meet some standard of social grace. I have shelled out a grand on some really nice attire that is comfortable and festive, but certainly not formal.
Why do I need to be formal on vacation? It sounds like Carnival agrees that the mainstream cruisers are there to relax and have fun.
I have toyed with the idea of getting a white jacket, but not sure it would be good fashion sense to wear that with white linen pants and a colorful shirt. For the other nights my Tommy Bahama shirts are kind of a "jacket" over my "artistic" T-Shirts. If I can pull of this white jacket deal I wont have to worry about dress slacks and shoes.