Formal night is becoming a thing of the past. I have read on numerous boards that cruisers are constantly trying to avoid formal nights at all costs. Celebrity has not made formal nights real customer friendly since for the most part lately they have not enforced their own rules for dress. The dress code for men on formal night is Tux/Dinner Jacket or Suit. More and more men are now opting for Sport jackets and very few on all cruises no matter the length or location are in tuxes. Also, they have within the past few months changed the rules so that all specialty restaurants are now "Smart Casual" every night. Adding to that is the change which now allows jeans into the the MDR. I think it is very telling when people are opting to eat in their room rather than go to formal night in the MDR.
Years ago, Celebrity requested that you remain dressed up for the entire evening in all venues.It seems now that the only place you are requested to dress formal on formal night is the dining room. The theater and all other venues are also "Smart Casual" as per Celebritys rules.
Just as in society we have relaxed dress standards (go to a funeral or a wedding lately) the cruise line standards are changing. Celebrity will be Smart Casual everynight, very soon.
The above does not express an opinion of how I feel about formal nights. I am only passing on what I have observed on board ship with two Celebrity cruises in the last year and also reading thousands of posts on various boards.