I wore capris (not denim) on several nights with a nice blouse- not tshirt. Theyare widely accepted as far as I could tell. The first night we were rushed and hubb couldn't get back to the room and met us at dinner in khaki shorts and a short sleeved shirt and so did several other people. They made an announcement that that was fine for the first night but on other nights they would not be allowed to dine in the sit down dining room.
So I'm not planning on where a dress every night. I'll wear a skirt one night, a dressy dress one night, slacks one night and probably capris the other 2.
Carnival Fantasy 6/05
RCCL Sovereign of the Seas 4/07
RCCL Navigator 12/07
RCCL Navigator 11/08
RCCL Liberty 7/4/09