Hi Darlene,
Yes, its true, during the day, you mostly just wear your swim suit, shorts, sandals etc. As for formal night, most women wear nice cocktail dresses and yes sleeveless is fine, but may-be have a sweater handy, sometimes the dinning rooms can be chilly. For some reason on our last cruise that was not the case, the dinning room was fine, but I still had a sweater packed just in case. You do see a lot of men in tux's or dark suits for formal night, gosh do they look good. If you already have a tux, just bring it along, my husband wore his and he didn't seem to mind. As for the kids, just nice dresses and nice slacks and shirts for the boys.
Here is a link to some great tips for taking your first cruise:
<http://www.cruisemates.com/articles/cruiseguide/first-time/index.cfm>
Enjoy your first cruise, bet it won't be the last either :-)
Donna
Tuesday Chat Host