Yes, there is what is known as "Express Departure". You carry your own luggage off the ship at about 6:15 a.m. We did it this last time and saved us a lot of time.
If you are flying with American, Continental, Delta, or United, and your flight is AFTER noon from Miami or after 2 from Fort Lauderdale, you can sign up for Luggage Valet and Onboard Check-in. This service costs $10 and must be signed up before Thurs evening. After you go through customs you leave your luggage with airline personnel at the pier and you go straight to your airline. They handle your luggage. We did this, and had no trouble at all.