I would try to get some type of airport shuttle/limo between MIA and Fort Lauderdale.
With Tri-Rail, it will be a bit inconvenient and you'll have to schelp all your luggage yourself.
I'm not sure where the closest Tri-Rail station is to MIA, or, for that matter, to Port Everglades!
Tri-Rail does have some delays ... but those seem to be on weekdays.
You might want to use Yahoo Yellow Pages to check on airport limo services.
I would definitely spend the night before the cruise in Fort Lauderdale. Traveling I-95 from Miami to Fort Lauderdale can be a nightmare if there is a traffic tie-up. Even on a weekend, all it takes is one overturned semi!!!
If you stay in Fort L., you can wake up, have a nice breakfast, and head over to Port Everglades at your leisure. Many hotels offer free shuttle service, too, which is nice.
I recommend the Marriott Marina [or is it the Marina Marriott?] on 17th Street Causeway ... if you're on a high enough floor, facing the right way, you can see the cruise ships in port!
Have fun!
