I wasn't going to say anything cause I don't want to sound like a know it all, but.... We went on a Caribbean cruise on Princess Cruise Line over NYE 2004/2005. It sailed out of Ft. Lauderdale and went to a couple of little Caribbean islands. When we arrived back to the port in FL on 1/1 everyone was waiting in the atrium by the exit doors to disembark the ship. And there we stood, waiting, and waiting. We booked a flight after the time Princess approved (I forget now, but I think te cutoff was 10am and our flight was 10:40am) and we missed the flight. So did many, many other cruisers with flights between 10 and 11 or so.
The problem was that there were a few international cruisers who had not handed in customs forms, or something like that. Well NO ONE was allowed to disembark until they found these 4 passengers (separate 4 people, not 1 party), and that took forever. They had customs agents board the ship and everything. The mob of people waiting in the atrium with their carryons quickly turned angry as people realized they would miss their flights. We had booked airport transfers with Princess but figured there was no way we'd have time to wait for a bus to load so we planned to get a taxi. Unfortunately about a million other people had the same idea, so by the time we found all of our luggage (and we got a porter to help too, but it still took quite some time as they were not even all together) the taxi line was way, way long so we headed over to the Princess buses. They got us on a bus and off to the airport pretty fast since we told them when our flight was, but we still missed the flight. And we had checked in online so all we had to do was check bags, but we were there within the minimum time to do that so no luck. And every flight out of that airport was booked till 1/5!!! So we called about every airline in the world, found a Southwest flight leaving the next morning out of Orlando, got in a rental car and drove the 3+ hours to that airport and got a hotel room.
Now I'm sure my story is a fluke, but based on that experience we will not book a flight with a borderline departure time after a cruise. It's just not worth the worry and then the hassle involved if you miss the flight.