I called Carnival to ask them about the formal nights, and I was suprised to find out that there will only be two. Same as a 7 night! I'm not complaing though, I don't like formal nights! As a matter of fact this will be the first cruise that we are leaving our formal wear at home and skipping the diningroom those nights. On our past 10 cruises we have participated in formal nights. I think the longer cruises like this one, are little more layed back.
There is a laundry room. I think it cost 1.00 to wash. I'm not sure what the dryers cost, usually they are less than the washers. Also there are ironing board and irons available(I can't remember if they are free or not.)
In the cabins they have blow dryers, so that's one less thing you have to pack!!
Well Good Luck! If you have any more questions, just Ask! (I've been on the Spirit once before!)