Hey there SirBigSur,
We'll be in Edisto for a week starting March 28th and leaving Easter. We LOVE it there!
You can see pics of our trip last year here:http://picasaweb.google.com/CampinPa/Edisto2009#
Edisto is broken up into two campgrounds. The BEACH loop and the LIVE OAK loop. The LIVE OAK loop is 1/2 mile from the beach and you may need to drive to get there. The BEACH loop is, as the name implies, right on the beach.
Sites 1, 3 and 6 are not really friendly for a camper. Sites 5,8,9,10, 12, 53-75 odd are the only ones that are really fully shaded. 16-50 are FULL SUN, so be prepared if your going in the summer months.
Hunting Island State park is another of our favorites. Most of my signature pictures are from these locations.
Hope it helps.