Anyone can join!
http://www.3fatchicks.com/forum/showthread.php?t=108322
Just hit reply with "count me in" type message...
The only committment, I think, is to post your WI same time once a week, every week, or you will be dropped out of the challenge. Also, trying keeping up with the diet you are on, since the challenge belongs on the main page, everyone is doing something different. ie LAWL, Calorie Counters, WW etc... They encourage you to add exercise, challenge you to drink your water, and more. There are several threads there form the previous challenge, that you can read up and figure it out.
To cut to the point - it's another layer of countability. Helps keep me in line, for now not only I let your girls/guys know of my weight problems, the rest of the 3FC knows, helps, advise, and encourages you.
Hope this helps a bit, I am no expert. And didn't do all that well in the last challenge. I believe our own KrispiD have done exteremly well at the last challenge!! Ending at the Second Biggest Loser!! Yah Kristen!!