Not sure what I'm talking about? I just went to my second this year (2011). I have to say that the Full Moon Party can only be described as completely unrestrained hedonism, chaos, and debauchery -- all under a full moon on a beach in Thailand. Perhaps one of the world's largest/greatest parties.
You'll love it and hate it at the same time.
Regardless, it's an experience.
Here's an article I wrote about the FMP: http://goasia.about.com/od/Events-and-Holidays/a/Koh-Phangan-Full-Moon-Party.htm
and here's a new one on the site by John Peden with insider advice for surviving the party:http://www.startbackpacking.com/travel/koh-phangan-full-moon-party/