Nothing much in Grand Turk apart from the cruise port. You could probably walk the whole island in the time you are there. Did a tour and saw a lighthouse with a nice view of the ocean. The cruise port was nice, with a nice beach and pool/party area.
Got a great zip-lining deal in DR. Took a taxi to the site for $15, and paid $50 to zip line. Carnival offered that excursion for $109. Was pretty good for our first time, but next time I want something a little more adventurous like mountainous rain forests or rivers or something (this was a wooded area off the highway).
Some of our group did a tour in La Romana and got ripped off. They took a trolley that was run by Carnival and paid $19 for a tour and beach trip (they paid using their sail and sign card). Turned out to be a 20 minute tour back to the ship! They got reimbursed 50% after complaining en masse.