My wife Donna and I are both Platinum level members and have cruised on Carnival almost every year since we met back in '99. Many of these were 3-4 night cruises (initially out of NYC and now Long Beach), but we have also done longer ones to the Caribbean. Carnival cruise #12 for us will be this coming October on the Splendor.
I won't say that every cruise has been 'smooth sailing' and we have had our share of small complaints. However, overall we are very happy with Carnival ships, crew and ports of call.
At this rate I may be spending almost at much time sailing on cruiseships as I did on a number of ugly, haze-grey ships when I was in the Navy.