The water taxi was a fun and interesting way to travel. Of course there was an "unpaid tour guide" who was to be tipped and Liz was nearly sick. But for me it was a nice ride and I took many pics along the way.
I doubt I'll ever be able to get on another one with her with me but I found it cheap and easy to use. It was $3 each way per person.
There's a daily ferry service that leaves Nassau for Harbour Island and stops in Spanish Wells on the way. There's only one ferry a day in either direction - 08:00 from Nassau and 15:55 from Harbour Island. The trip takes about 2hrs 15mins and costs approx $110. This means you have about 6hrs on the island which is ideal to see everything and relax on Pink Sand Beach (see my Harbour Island & Dunmore Town pages for more details). The ferry terminal in Nassau is located near Bay St under the exit bridge to Paradise Island.
You can actually travel around the Bahamas by Mail Boat. They have a horrible reputation for punctuality and generally just aren't used, but you can do it for a pretty good price. Other than the mailboat, your option for inter-island travel is pretty much limited to air. There is one high speed ferry that hits two or three main islands, but costs as much as a plane ticket. The mailboats aren't quite speedy either, as you can tell by the times shown in the schedule above.
If you are sightseeing in Nassau and staying on Paradise Island, they have a small water taxi service. For $3 they take you to the marina where it should be a short walk to the major hotels. The reverse trip takes you to the quay wall near the straw market.The only problem with this is that the boat won't leave until its pretty full, so look for one that already has quite a few people aboard. They run until six.
A local ferry is available from the Atlantis Hotel across the harbor to the Straw Market area of Nassau and back. It only costs $2.00 and is a great way to see the harbor and the downtown coastline.