A new travel book--The Naked Truth About Cap d'Agde (by Ross Velton)--just came out in May 2003. It answers a lot of travel questions about Cap d'Adge and explains the activities you can expect among the libertines (swingers make up about 1/3 of the guests to the resort won) and the family-style nudists (who are the remaining 2/3 of guests).
An excerpt of the FAQs about Cap d'Agde from the book is at http://www.wordcrafting.com/ --just click the book and then click the Cap d'Agde pulldown menu for Book Excerpt.