As of 2007, it is required for all visitors to the BVI to have a valid passport from their country of origin. When you enter into immigration & customs you will need to have your passport ready and the necessary forms filled out (you'll be given these on the ferry/plane and will have time to fill it out, takes about 2-5mins, one form per family name is required and covers all the people in your party under the same last name). You will also enter in customs after being stamped and cleared by immigration where you will collect your luggage and pay any duty fees (if you declared things you purchased in St. Thomas on your form for example you will pay duty on it in bvi customs).

After doing that, they may or may not check your bags, it's usually a random check like security in the U.S and Europe perform, you're home free. There are taxi driver's waiting outside of customs both at ferry terminals and the airport, so that is never an issue.