Back from my trip...I spent a weekend on Isla de la Juventud. Since there seems to be next-to-no info about Cuba on this forum, I thought I'd post a short trip report.
The island is off the south coast of Cuba and can be reached by either a catamaran or by a 35 minute flight from Havana, which is how I got there. If you do fly, get to the airport early! When you get to Isla de la Juventud, you'll be in the principle town on the island, Nueva Gerona, on the far north. The diving marina is about 30 miles to the south, just down the road from the one hotel in the area, the hotel Colony. The Colony is basically the only choice for anyone wanting to dive on Isla de la Juventud, and it's perfectly acceptable for anyone who is only looking for a decent room, passable meals, and lots of peace and quiet on the beach. The strange thing is that it seems to be mostly vacant for much of the year. I was the sole guest in the entire hotel when I checked in.
The diving is on a point about 15 miles from the marina called Punta Frances. There are lots of sites, mostly shallow, but a few walls where you can easily get as deep as you like. Visibility on the day I dove was around 60 ft, but I suspect it's normally better. It's pretty typical caribbean coral formations, not especially healthy, but some nice sponges and soft corals. There is the usual variety of small reef fishes with a few larger angels and groupers, lots of big green morays, and some nice sized lobsters.
The boat is about 40 ft, very comfortable, and slow.....As in the hotel, I was the sole client that day, along with a DM, captain, and cook. The best meal I had on my entire trip (including a week in Havana) was the lobster lunch on that boat on the way back to the marina. It's an hour or more to the reef from the marina. The reef was completely empty of other boats and divers. This place is seriously remote compared to other caribbean dive sites I've visited.
The crew was friendly and professional. We used AL80s with either DIN or yoke connections. I had an interesting conversation with the DM about the challenges of getting and maintaining quality dive gear in Cuba; I ended up leaving him a MK15/balanced-adjustable as a tip. I'm sure it was a losing proposition for them to take a 40ft boat on an all-day trip with only one diver!