My girlfriend and I went on our second cruise w/ Carnival (our first cruise was to Ensenada on the Ecstasy) and had a BLAST!
We had to fly to Orlando a day early because there wasn't a flight out of San Diego early enough. So we stayed at the Clarion Hotel a couple of miles from the airport. The hotel as well as many others provides transportation to and from the airport at no cost. (They can also drop you off and pick you up at some of the nearby restaurants).
The next day we took the free shuttle back to the airport and took the Mears transportation service to Port Canaveral. The bus was packed to the max w/ cruisers. The trip took about 45 minutes and the seats were more comfortable than the seats on the plane. The Carnival staff at the airport was very nice and courteous.