I dove the Caymans one trip. I wouldn't go back there until things get back to normal, and the reefs will likely be debris-cluttered due to Ivan for a couple of years, too: but it's still one of the great dive spots in the world. Though I didn't get there (it's an all-day trip from Cayman Brac, which I did dive), Bloody Bay Wall on Little Cayman was rated one of the top 10 diving sites in the world. Most Cayman wall drop-offs start at 60-80 feet; Bloody Bay Wall starts at 30 feet.
I didn't try to view the high-resolution mural, but if you've got time it might be fun.
