Yahoo groups have some possibilities. You might also try NaNoWriMo.org as one of their forums relates to writing erotica. I put a site up through yahoo a yr or so back that focus's mostly on NaNoWriMo and erotic writing. Not much activity there though I have collected a lot of links, some of which you might find of use.
http://groups.yahoo.com/group/NaNoRotica/