I agree, Jun. There is a potential for liability problems that can't be anticipated until they come up. I would worry that creating such a forum implies acceptance of liability on your part for the advice provided by the posters. I'm not an attorney, so this should also not be considered legal advice!
Yeah, I know, drkoop.com handles it differently. But do you know how many lawsuits are currently being settled with them? No? Then I think better safe than sorry.