Slander, no, libel...maybe. Libel is the publication of a false statement, (and is not a privileged communication) which injures one's business or personal reputation. It is up to the "plaintiff" to prove such damage.
It is not libel if the statement is a true fact or an opinion, as in, "I think so-and-so is a crook." rather than, "So-and-so is a convicted pedifile." (where in fact so-and-so is not.)
A suit can be brought against the originator of the statement, those who pass it on, and/or the service provider or the administrator of the web site. I'm a little surprised no vendor hasn't gone after the administrators of ClubGP!
I love law, I'm finishing my MBA this year and looking to start the NIU School of Law the Fall of 06'. Hopefully in a few years I can charge for information like this.