You definately need to be on your toes when it comes to shopping in the jewelry stores in Nassau, St Thomas, and St Maarten. These people are professionals and would sell you the shoes on your feet if possible. They are pushy and rude. My fiance and I were looking for wedding rings and while we did see some stuff we liked, but got tired of the rude people behind the counters. One store was a Carnival approved store (where they did one of the drawings) and we had about 5 lowest price manager offers on the same ring and then the manager was quite rude when we didnt purchase the ring. To be honest with you, I wouldnt have trusted it to be gold, much less a real diamond. And while Carnival says they will gurantee anything you buy from an approved store (RCCL said the same thing), it's going to be quite difficult to get a problem fixed when the store is in St Thomas (or other) and you are in the states. The best thing was when you walked in many of the stores were the free drinks they offered the men, hoping to get them buzzed and then they would tell the wives to buy what they wanted.
We ended up buying our ring at the Navy Exchange in Jacksonville, got a great deal, larger diamonds, and no sales tax and we trust what we purchased and it would be simple to fix any problems that may arise. Definately knwo what you are buying before whipping out he plastic in the islands.
As far as booze is concerned, that was a good deal. We hit Al Cohens in St Thomas (by the ship) and got some good prices, especially with the additional 15% off on 4 bottles or more. We were also informed by a customs person who said you could bring in 9 bottles/person before they would bother to fill out the paperwork to charge you anything.

CCL - Oct 08 - Glory
RCCL - Dec 07 - Grandeur of the Seas