Dunns River Falls, is great. That's in Ocho Rios. If you prefer not to climb the falls themselves, you can go along the side. Climbing the falls is a blast, you need water shoes. The guides will hold your camera for you and take pictures on the way up. The water is cold and refreshing. The time we were to stop in Haiti, they rerouted us due to a military coup going on. This was years ago, so I can't help you there. You don't have to do the excursion to Dunns through the ship, though I highly recommend doing so. Jamaica is a beautiful country, but very poor. Stay in a group no matter what you do. It is one island I strongly urge people to do a ship's excursion. It's just not wise to go out on your own there. If you do, be sure to stay in the tourist areas.
I took this cruise in April, 07. No need to do an excursion in Haiti. It's a private beach owned by the cruise line. Your ship account card works there, like being on a private island. We did choose to take the walking tour. It's the only way you'll get any feeling for the culture and history of Haiti. But, if you're interested in beach style sun and fun, just go and enjoy.