My older two kids did it in 2006, and it was their #1 favorite thing of the entire vacation. So much so, that they went again last August. They really, really loved it, and at one point, were literally flying with an eagle!
A few tips: We booked only a few days out from going. We planned all the rest of our trip, then schedules. It's best to go in the morning, as you can't do it when it rains. Also, scheduling it so close gives you a weather report that's fairly accurate. I know you already scheduled, but re-scheduling should be no problem if your other plans change.
You don't get wet. We brought suits, but the kids stayed dry--took off and landed on the boat.
There are minimum and maximum weights, so my kids (11 and 13 last year) went tandem. I swear, I could hear them bickering from the ground!
If you bring a camera, I suggest a waterproof, one-use one, just to be safe. Use the wrist strap!
My kids went out in the boat with another couple, and I believe there was room for just DH to go on the boat with them (he didn't parasail). there may be different prices dfor tandem/solo, and possibly different heights/sailing times. The first time, we were on a plan (premium, maybe?) that included watersports, so it didn't cost us anything. Last time, it was a gift from their grandmother. I'm thinking $185 (generous grandma!).
I hope that helps you. I'm way too chicken to go myself, but the kids couldnt' say enough good things about it.