Re: Cayman Brac - my new wife and I just returned from 10 days there (honeymoon) and it was wonderful. The diving was spectacular. We dove with Reef Divers (one of two dive operations on the island). They were excellent - very professional and customer-oriented. Shore diving is possible all over the island, except that the somewhat rocky bottom can be tricky to navigate from some places. I think the south shore (there are a few public beach/access points) would be preferable to the north shore for shore diving. The water tends to be rougher on the north side.
Cayman Brac is a very small, quiet island with only a few restaurants. However, the scenery is magnificent, the snorkeling and diving is world class, the food is great and the people are warm and friendly. We stayed on the north shore at a house called the Lankford House, owned by two Americans who now teach school on Grand Cayman. The rates were extremely reasonable and it was totally private and comfortable. I would be happy to send you (or anyone) their contact information - the house is immaculate, right on the water (I mean RIGHT ON THE WATER) and has everything you need to enjoy your stay there.
Cayman Brac is very hospitable so long as you are not looking for a ton of shopping, movies, etc. They have cable/satellite TV and a few bars but that's about it. If you are looking for a quiet relaxing time, then I highly recommend Cayman Brac. If you want a tourist destination, then I would suggest another place!