On Carnival Triumph and Conquest.....make sure you get an early seat at the comedy shows. I've noticed that they didn't use a bigger theater for the shows and less people were able to see the shows. When I was on Carnival Ecstasy in 2005, the comedy show was in a bigger theater....oh well, I guess things have changed since then.
RCCL you have to book your tickets. We missed out on our last cruise on the allure (my BF parents did the stand by and got in), but this go around, I booked every show... here is to hoping!
But I did notice it was the smaller theater too...