My mother and sister lived on St Thomas for 2+ years. Visited them many times and have been back since they returned to the states. Actually my husband and I will be there again in February. For the beaches:
Coki is great snokeling but very crowed when cruise ships are in port. There is a great beach "restaurant" called Buddy's at one end of Coki that serves delicious local food. I don't know which is better, the food or eating the food outside right on the beach. Magens is dubbed one of the 10 most beautiful beaches in the world by National Geographic. It is a very pretty beach but again has a lot of visitors although it is longer and wider than Coki therefore holding more people comfortably. It has a very large bar for food and drinks and you can rent chairs, etc. Not good for snorkeling. If you really want a treat on St Thomas, get off the ship and get a taxi to Crown Bay Marina. This is on the West end of island going toward airport. From there find Tickles Restaurant (you will see it) and take water taxi to Water Island. From the ferry dock it is a short walk up the hill and then down to Honeymoon Beach. The name says it all and most likely you will be the only ones there. Occasionsally the Kon Tiki makes a visit for a few hours. You will find sea glass along the beach that is rounded and smooth by the tumbling over the water and coral. Also nice shells. If this sounds to adventureous for your day trip, you can take a taxi from the cruise ship dock to Brewers Bay beach. This is a locals beach however, not many locals are there except on weekends. Even then not crowed. A local wonam drives a truck adapted for cooking and you can enjoy fresh pates (a fried meat or fish or vegetable "stuffed pocket") and dollar beer. We were there one time and the local minister from St John had not one but two differnt weddings right on the beach. Both couples were from cruise ships. I watched the local park service men shake coconuts from a tree here one day. When asked, they cut the end off of one for me to enjoy. What an experience. You just don't find this in the tourist spots. Good shelling too. If you have already been to Trunk Bay and decide to go to St John (a great chioice) BE SURE to rent a jeep. Since the island is vey small you can see the whole thing in a short time. There are so many beaches there along the National Park north side. Over by Trunk is Caneel, Francis, Maho, etc. All are great! But then you can head up to Annaberg and see the sugar mill ruins all while you are overlooking Tortola, BVI. At the other end of St. John is Coral Bay a great place for lunch right on the water. Lots of sailboats here with transits and live aboards. Salt Pond Bay is close by and another must see. Good shelling. The drive on St John along Centerline drive (I think that's the right name but there is not enough roads to get lost) is breathtaking. You just cannot believe how beautiful it is but, if you don't rent a jeep or take a private taxi tour (which is readily available at Cruz BAy ferry dock) you will miss it. Hope I have not bored or overwhelmed you with my input to your request. It has been almost 3 years since we were there last and now that we have made plans to go in February for 11 days I can hardly stand myself!!! I must ask you though. Why are you taking a cruise again? My first visit to the Virgin Islands was also on a cruise ship. When I returned the first time many years later to vist my family, I realized just how little you actually see of an island when you are only there for a day. On our last visit, we stayed on St. Thomas and actually made day trips to St John, St Croix, Tortola BVI and Virgin Gorda BVI. You can still see other islands but have so much more time actually visiting them. I know the ship in itself is a lot of fun and relaxation but since you enjoyed Trunk Bay so much think how nice it would be not to have to get back in time for the ship to depart at 4:00. Anyway, I know you will have a great cruise. They are very nice. Please feel free to respond. I love talking to people that love the islands. (Guess you figured that out!!)

Wow! Thank you for all the info. You asked why we are cruising again. This is our 6th cruise to the carribean. We were supposed to stay on St. John this year with another couple we cruise with, but the places we found on the internet to stay, were much more expensive than the cruise.
We are taking the 7 day cruise for $600pp and only paid $500pp for air from the U.S. (California) to San Juan. The cruise includes all our meals. We're 46 and very young at heart. We love pushing it to the limit, seeing as much as we can in 6-8 hours. Yes-time can be a problem. We were almost running to the dock from town after our visit to St. John, but that's part of the fun! It also allows us to see a little bit of paradise here and there and decide where we will return.
Thank you for the reply, can I email you with a couple questions about Water Island?
Linda Larsen