CK--Orient Beach is a lot of fun! My bf and I went to St. Martin 4 winters in a row and stayed at the other end of the island--Cupecoy, which is supposed to be the "gay" nudist beach, but it's actually mixed.
We went to Orient Beach a few times to see how the other side cavorted, but we never went inside the resort itself--which, I believe includes nudity in the dining room!
But the best thing about St. Martin is the world-class French restaurants in the towns of Grand Case and Marigot. You're on the beach all day, then eating incredible food at night.