We were on the "Magic-al Mystery Cruise" of September 2002 - when the Magic was diverted by Hurricane Lili - we had two CC days, St. Thomas and San Juan!!
It was wonderful! We were able to go through the town, gamble and just take in the great sights that my mother's brothers told her about years ago when they were stationed there in the military!!!
There are some great excursions also - one to the Rum Factory (which I kick myself now for missing out on!) and another to the Forts.
Do not miss the sight of entering the harbor because you will pass the fort (left side) as you do so - it's spectacular!!
Enjoy!
Rae