Nancy, I have asked the same question, and other cruisers answered that formal nites now tend from long gowns & cocktail dress to fancy pantsuit.
I'm cruising (first time!) on the Vision in August. For formal nites (2), I plan on wearing black palazzo silk pants (very flowing, comfortable & loose) with a beaded top & slip-on sandals. For the 2nd formal nite, the black palazzos with a long-sleeved black shirt that has sheer sleeves and back, with a blank camisole underneath, with black slip-on sandals. The other nites i plan on wearing black dress pants with different tops.
hope this helps.
joanne