We stopped at Key West in October of 2000 due to Hurricane Joyce. We booked the Fury Catamaran sail and snorkel for the afternoon. I thought it was very enjoyable. The catamaran was petty large, probably holding 50 people or so. They took you about 7 miles out to sea and anchored off a reef which has a national park designation. We were there for probably a few hours. They have an open bar (beer, wine, soda) for the trip home (actually, the bar is always open, but they won't serve you alcohol until you're finished snorkeling).
I don't know if this will be one of the standard offerings, since ours was an unscheduled stop, but I thought it was a great snorkeling trip. I think we paid $49/person.
