You don't have to go formal. That request is for the Main Dining Room. You can still wear casual clothing in the food outlets on board. Formal can mean anything from full tuxedo for the men, floor length gowns for women, to suit and ties and cocktail dresses or smart suits for the ladies.
80/90% of passengers going to dinner on formal nights will observe the formal code on RCI ships. ... Neil.
I echo Neil's answer. Vast majority make the effort (and very nice they look too) If you are cruising out of Italy or Spain then the Continentals are very very smart on even the non-formal nights also I found.
Formal Nights have been formal for many years with us & hopefully will remain so. Regards Wilba.
I travelled on Voyager of the seas in August and found that it really was your choice. On the formal nights some men dressed in Diner Suits with Bow Ties and Tuxedos and Ladies in Cocktail dresses, and some wore smart trousers and shirts and ladies in black trousers and smart tops, saying that others in the lifts and public areas were still in shorts and t Shirts on formal nights and no one really cared. We chose to dress up and then later on after dinner, put casual clothes back on. The dining rooms did have mainly formal attire on the two formal nights but certianly not everyone adhered to this. You can always eat in the buffet if you do not want to go formal.