I've only been on carnival but they opened up the dining room for breakfast and lunch. All they ask is no swimsuits. Shorts are ok to wear in there. Its like regular dining with menus etc....
Life is too short to let the ship of your dreams sail without you.
Carnival Destiny Feb. 2006
Carnival Fascination Feb. 2007
Royal Caribbean Grandeur of the Seas Feb. 2008 The DTW & MsBJ tour
Carnival Valor MsBJ and Dina Feb. 2009
Carnival Glory MsBJ and Dina Feb. 2010
Carnival Dream MsBJ and Dina Feb. 2011
To add to dina's post, on most cruiselines, one of the dining rooms is open for breakfast and lunch and it is "open seating" dining. They put you at tables with others until they are full, then start another table. On some cruises, while in port, they were closed for lunch so we just had the buffet option or eating in port.
Teresa and Larry
#36-Carnival Splendor 9/16/12
7 night Mexican Riviera
#37-Allure of the Seas 11/11/12
7 night Eastern Caribbean