I was on the Carnival Glory in November. I don't know the specific name of the dock in St. Maarten that the Carnival Glory docked at. But it was in the city of Phillipsburg. It was a rather large dock area that accomodated 4 different cruise ships at once (one of which was the Glory). The other three were the Carribean Princess, Explorer of the Seas, and Carnival Victory. There was a fifth cruise ship the Sea Princess, which was anchored off-shore and used tenders(smaller boats) to get the passengers ashore.
St. Martin or Sint Maarten (as it is spelled on the Dutch side) is an island share by the French and Dutch. Phillipsburg is located on the south-east side of the island on the Dutch side. Marigot is located on the Northwest side of the island on the French side. You will have to get on a bus or taxi-van to get to Marigot. I went to Orient Beach (on the French side) in a taxi-van (the price was around $12 if I remember correctly). The road trip was not a pleasant expierience, since the middle of the island appeared poor and quite "Third-World" like. As a result, the road ways are rather undeveloped (not up to the standards I am used to in the U.S.). But everywhere near the coast line was nice.
The shopping in Phillipsburg seemed to be really good. I don't drink alcohol, but I did buy a bottle of Appleton Rum for my Jamaican co-worker back home. The price for a full liter was $7! Back at home I found the price was three times that amount for a 750ml bottle (25% less volume). I bought that bottle in the duty free store close to the cruise ship dock in Phillipsburg.
I hope this helps. Have a good time on your cruise.