We did this back in '99. We walked off of the dock and ran into the horse drawn carrage area so we decided to take the "tour" of the town in one of them. Ooops, that was our second mistake in Nassau (the first was getting off of the ship). The "tour" was a race to see just how fast the driver could get back to the dock to pick up the next suckers...er...I mean tourist dollars.
We couldn't hear the driver very well. And when we could hear him we couldn't understand him. He spent most of the time yelling to friends on the street or yelling at other trafic to get the $*% out of his way.
Once back at the "stables" his cohorts in fraud insisted on taking our picture with our camera and wouldn't give it back untill we gave them a significant tip. No, we didn't offer our camera to them, they took it from us as we were exiting the carriage.
It could be a very fun experience if you can hook up with someone reputable ahead of time and arrange for the tour. The city has a lot of interesting landmarks.