We happenned to be on the same cruise as well. It was absolutely out of this world. I am sure most of this was repeated already on the board and I'll try to get into more detail by posting a report, but here's what we experienced.
First of all, we discovered that getting your documents in order ahead of time makes a difference. When we arrived at the port there were about 40-50 people ahead of us on line waiting for the gate to open. However, once we cleared security we saw that most people did not have their Bahamas immigration forms filled out, so basically there was only two people on line at check-in. Since we filled out our forms the night before, we were able to get right in line and we were the second family checked in. This also allowed us to be the second family in the general boarding line to walk onboard, which in turn allowed our DS to be the first one in the pool and on the water slide and we had our choice of prime seats by the pool. So long story short, a little preparation can go a long way.
Second, as many others have said, be prepared for a little uneasiness the first night. Once the ship leaves the Gulf Stream you should be fine, but we noticed a lot of people not ready for the slight rocking of Florida waters. Take a look for either Bonine, the Less Drowsy Formula of Dramamine, or the prescription patches. There have been some good threads on this as well. The rest of the days were smooth sailing.
Next, Nassau is a hit or miss type of excursion. If you have never been there, there are some great things to do, such as the dolphin encounter, the straw market, the pirate museum as well as Atlantis. We booked a room at the Comfort Suites next door to the Atlantis for the day so we could have access to all of the facilities at the Atlantis as well as having a place to change and shower. However, since we had already visited Nassau before and we actually started to miss being on the ship, we wound up returning to the boat at about 1:30 PM, which worked out well since our DS joined up with the Oceaneer Lab just in time for a tour of the bridge. I think next time we'll just stay on the boat and take advantage of the low crowds and activities on board.
Castaway Cay was a different story altogether. From the moment we stepped off the boat we felt a world away from Nassau. Even with the tram the main section of the island is very walkable, especially in the morning when the temperatures are still reasonable. We followed the suggestions here and got up early to be one of the first ones off the boat and had our choice of seats with both an umbrella and hammock next to us, and no lines for snorkeling and float rentals.
The Pirates in the Caribbean party was a blast, literally! It starts out in the dining room and ends on deck 9 with a late night buffet and fireworks shot right over the ship while we were at sea! We were later told by the cruise director that Disney is the only cruise company that has permission to shoot fireworks at sea from the ship. All in all the evening was great and a wonderful photo opportunity. Many of the characters even join in the fun and dress up in pirate gear.
We did both the Palo dinner and brunch, and loved them both. You almost never want the experience to end. The dinner is incredibly intimate and romantic (there was even a marriage proposal at the table next to us!), and the brunch was to die for. Not only did they have all the Alaskan king crab legs you could eat, but they were also already pre-split for you, so all you have to do is enjoy them. If only I could take the restaurant home with me...
Our DS loved being the the Oceaneer lab, but also enjoyed time with us as well, so it was a good balance. He wasn't keen on the goodbye show, so we didn't push it. Plus it gave him more time to be in the pool, so he was happy about that.
One thing to keep in mind that we spent a week at WDW before the cruise, so the cruise itself did not seem rushed. I think if we would have traveled to Florida just for the cruise, it would have seemed too short and perhaps been a little more sad when it was over. But with us doing a week in the parks ahead of time, we were ready to go home once we were back at port.
Once more thing to remember...without a doubt, you WILL spend more that you think you will. With all the souveniers, the drink specials, the photo shoots, and the dreaded bingo, your bill will be noticably different than what you imagined. Trust me, I never thought I would be spending any additional money there, but believe me you will. Just a warning.
Hope this helps. If there's anything else I can remember I'll be sure to add them in.