I loved diving in Cuba, even though I was in the process of getting certified at that time and just did shore dives. There was lots of colourful coral of varying health and abundance, wall diving, lots of fish, lots of swimthroughs, warm water, great visibility...
The people who did the boat dives were thrilled with their dives.
I've heard the Bay of Pigs (Bahia de cochines) is awesome diving - yes, THAT Bay of Pigs of U.S. - Cuban History fame. Cayo Largo and Cayo Coco are beautiful and semi-secluded - incredibly beautiful to visit but not sure how the diving is there, though.
We found Cuba to be incredibly beautiful. We stayed in Varadero and visited Havana as well as Cayo Largo before there were any hotels on that island. We visited Playa Serenas on Cayo Largo, one of Conde Nast's Top 10 most beautiful beaches in the world - and were awed by it's pristine un-clearcut beauty. We found the people very warm, friendly and helpful as well. I would like to visit again sometime to dive a lot more.
You should do a google search on "cuba diving" and I'm sure you'll get specifics and helpful info. Have fun!
BTW, this is the Accidents and Incidents Forum - perhaps this thread should be moved to the Caribbean?