Florida tips
Lucky ol' you, You will love it. I went about 5 years ago (for the kids!) and was quite cynical of the whole Disney thing beforehand. However, once you're there you can't help enjoying it.
Disney's Magic Kingdom is really ideal for smaller kids, say 4-10, or sentimental adults! However its star attractions, Space Mountain, Splash Mountain and Big Thunder Railroad are worth a visit and will not disappoint teenagers. If you want to take in these, GET THERE EARLY in the morning. Remember, Disney's parks open an hour before the advertised time (ostensibly a 'privilege' for guests in Disney's own Hotels/Resorts, but in fact, available to all. If you do this, you can reduce the queue for Space Mountain etc. to a few minutes, rather than the couple of hours it will take later in the day.
Disney's EPCOT and MGM Studios would appeal to older kids or teenagers (although personally I found MGM the most dissappointing of the theme parks, no rides and LOADS of merchandising.)
The nightly EPCOT laser/fireworks show is AMAZING and well worth a visit.
Universal Studios is better than MGM, and definitely has better rides.
The Daddy of them all is BUSCH Gardens. The roller coasters are truly amazing and unforgettable. If this don't scare you nothing will. Big cojones required!
Also well worth a visit are the water parks. Wet-n-wild is near Disney and is fabulous fun with some incredible water slides etc. Teens will love it! Think Tralee Aquadome to a factor of 100 with weather!
Elsewhere, Kennedy Space Centre (about 60 miles from Orlando) is unmissable if you have any interest in Space or Astronomy. If you go, do take in the guided tour of the launch pads and the Apollo launch centre. The sight of a fully equipped, real (unfired!) Apollo rocket is awesome.
Daytona beach will be in demand by the teens, but you may need to lock up your daughters!
Disneys Animal Kingdom opened a couple of years ago has got good reports and might be worth a visit.
Financially, do NOT buy tickets for the attractions before you go. They are ALWAYS cheaper, and sometimes heavily discounted, in Florida. The 5 day Disney pass is good value.
Do NOT stay in a Disney hotel. They are twice the price of anywhere else and offer very little for it.
For getting around, a car is essential, and air conditioning is pretty universal. Avoid the pressure to upgrade to an even bigger car - they always try this!
For shopping, there is an excellent outlet mall at the top of International Drive - I can't remember the name. Really good designer stuff at great prices - kids, teens and adults all catered for.
Finally, you should pick up the Fodors Guide before you go - they do one for Walt Disney World and one for Florida. They are very accurate and 'tell it as it is'
Enjoy!