We did the QE2 last year. In 14 days, we had 8 formal nights. Wear the same pair of black trousers and alternate about 3 or 4 tops. Nobody notices except you. The rest are smart casual (ie no jeans but a jacket) They always have informal dining available but being with the others is part of the fun. One word of warning, Cunard is very class conscious. The higher the grade of cabin, the higher the grade of resturant, but the food is meant to be the same throughout. Enjo.
Go onto their website. All is there for the reading!!