We were on Triumph in February and there were still quite a few people dressed "elegant", but very vew dressed "formal". We did not see anyone that was offensive, but when on the Fascination in October 2008, our table mates were... well... I guess "just a little bit country" would best describe them. On formal night, the gentleman wore a golf type shirt under his overalls which was a dramatic improvement over other nights.
I think Carnival has migrated from formal to elegant to accomodate those who do not feel they should have to dress-up, or for those who packing may be an issue. I will align myself with a previous poster and say I do not advocate one way or the other, but I did read a post a while back from a mother of 4 who stated that if she packed for formal night, the only time the shoes would be worn would be formal night, and she could not justify taking 6 extra pairs of shoes (herself, husband, and 4 kids) just for one night, so I guess I can understand that.