I've been on 2 cruises. One last Dec, over Christmas (wonder), and one just like a week ago, March 15-22 (magic)
All I can say is wash your hands, a lot!! We went on a second one so soon because on the first one me and my brother got really sick.. not seasick, but the GI sickness that makes you puke your guts out.. NOT fun. We were quarantined for 48 hours (keep in mind this was a 4 day cruise..) so missed half of the cruise, it sucked except we were able to get off at the two ports of call (Nassau, and
Castaway Cay) which was awesome.
I was seriously OCD about germs and went to find wipes all the time (they give them to you before all your meals, but we washed our hands in the bathrooms first also) and the whole time i touched probably about 6-7 doors during the whole 7 days, not including our stateroom door. I let other people touch them, or i used a wipe to grab it

Same with the ice cream machine, i always used a wipe, and elevator buttons..
Anyway, I probably was a little too paranoid, but none of us got sick this time!!

Its also possible we got sick from the airplane.. or possibly our waiters. I honestly think the staff is part of the problem sometimes. At our first cruise I went to dinner the first night, was sick the second as was our waiter.. although i guess its possible we got him sick too, lol. They come back after like.. one night, Im sure they are working while they are still contagious.
Overall the cruises are SO much fun.. one of my favorite things was the karaoke! And the food is (mostly) awesome.. I got some fish thing I did not like, but especially some of their pasta stuff is AWESOME.
Personally, I did not really enjoy the teen area.. but thats just me. I went up to the Stack (on the Magic, its the Loft on the Wonder) a few times and met a group of people that were really fun to talk to. I saw them numerous times around the ship too. I mainly didn't go up there because my sister and our friend (who we know from school they happened to sign up on our same cruise!) both of them are pretty quiet and they actually NEVER went up to the Stack

I usually was with them.. lol we spent a LOT of time in the store.. kind of sad actually. Our friends sisters however spent almost the whole time up there, they loved it.
Also make sure you go to all the evening shows! They are all REALLY good.
Its almost impossible to not have a great time on any
Disney Cruise! (Unless of course you get sick.. lol) You'll have a blast!