Yup they have one "Elegant Night" on a four day cruise. They stopped doing formal night and the dress standards have been relaxed. So all you need is dress slacks, dress shirt, and a sport coat. In fact I was on one of the first cruises with this relaxed standard which just happened April 26, 2008
Here is from the website:
"Cruise Elegant Dining Dress Code: Gentlemen - Dress slacks, dress shirts. We also suggest a sport coat. If you wish to wear suits and ties or tuxedos, by all means we invite you to do so. Ladies - Cocktail dresses, pantsuits, elegant skirts and blouses; if you‘d like to show off your evening gowns, that's great too! Not permitted in the dining room during the Cruise Elegant dinner for ladies and gentlemen: shorts, T-shirts, beach flip-flops, bathing suit attire, jeans, cut-off jeans, sleeveless shirts for men, sportswear, and baseball hats."